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THE FAUNA OF BRITISH INDIA,

INCLUDING

CEYLON AND BURMA.

Published under the authority of the Secretary of
State for India in Council.

EDITED BY A. E. SHIPLEY, M.A., Sc.D., HON. D.Sc., F.R.S.

FRESHWATER SPONGES,
HYDROIDS & POLYZOA.

BY

N. ANNANDALE, D.Sc.,

superintendent and trustee (ex officio) of the indian museum,
fellow of the asiatic society of bengal and of the calcutta university.

LONDON:
TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.

August, 1911.

PRINTED AT TODAY & TOMORROW'S PRINTERS & PUBLISHERS, FARIDABAD

CONTENTS.

EDITOR'S PREFACE.

Dr. N. Annandale's volume on the Freshwater Sponges, Polyzoa, and Hydrida contains an account of three of the chief groups of freshwater organisms. Although he deals mainly with Indian forms the book contains an unusually full account of the life-history and bionomics of freshwater Sponges, Polyzoa, and Hydrozoa.

I have to thank Dr. Annandale for the great care he has taken in the preparation of his manuscript for the press, and also the Trustees of the Indian Museum, Calcutta, for their kindness in placing material at the disposal of the Author.

A. E. SHIPLEY.

Christ's College, Cambridge,
March 1911.

SYSTEMATIC INDEX.

GENERAL INTRODUCTION
TO THE VOLUME.

Although some zoologists have recently revived the old belief that the sponges and the cœlenterates are closely allied, no one in recent times has suggested that there is any morphological relationship between either of these groups and the polyzoa. Personally I do not think that any one of the three groups is allied to any other so far as anatomy is concerned; but for biological reasons it is convenient to describe the freshwater representatives of the three groups in one volume of the "Fauna."

Indeed, I originally proposed to the Editor that this volume should include an account not only of the freshwater species, but of all those that have been found in stagnant water of any kind. It is often difficult to draw a line between the fauna of brackish ponds and marshes and that of pure fresh water or that of the sea, and this is particularly the case as regards the estuarine tracts of India and Burma.

Pelseneer[^[A]] has expressed the opinion that the Black Sea and the South-east of Asia are the two districts in the world most favourable for the study of the origin of a freshwater fauna from a marine one. The transition in particular from the Bay of Bengal, which is much less salt than most seas, to the lowerreaches of the Ganges or the Brahmaputra is peculiarly easy, and we find many molluscs and other animals of marine origin in the waters of these rivers far above tidal influence. Conditions are unfavourable in the rivers themselves for the development and multiplication of organisms of many groups, chiefly because of the enormous amount of silt held in suspension in the water and constantly being deposited on the bottom, and a much richer fauna exists in ponds and lakes in the neighbourhood of the rivers and estuaries than in running water. I have only found three species of polyzoa and three of sponges in running water in India, and of these six species, five have also been found in ponds or lakes. I have, on the other hand, found three cœlenterates in an estuary, and all three species are essentially marine forms, but two have established themselves in ponds of brackish water, one (the sea-anemone Sagartia schilleriana) undergoing in so doing modifications of a very peculiar and interesting nature. It is not uncommon for animals that have established themselves in pools of brackish water to be found occasionally in ponds of fresh water; but I have not been able to discover a single instance of an estuarine species that is found in the latter and not in the former.

For these reasons I intended, as I have said, to include in this volume descriptions of all the cœlenterates and polyzoa known to occur in pools of brackish water in the estuary of the Ganges and elsewhere in India, but as my manuscript grew I began to realize that this would be impossible without including also an amount of general introductory matter not justified either by the scope of the volume or by special knowledge on the part of its author. I have, however, given in the introduction to each part a list of the species found in stagnant brackish water with a few notes and references to descriptions.

Biological Peculiarities of the Sponges, Cœlenterates, and Polyzoa of Fresh Water.

There is often an external resemblance between the representatives of the sponges, cœlenterates, and polyzoa that causes them to be classed together in popular phraseology as "zoophytes"; and this resemblance is not merely a superficial one, for it is based on a similarity in habits as well as of habitat, and is correlated with biological phenomena that lie deeper than what are ordinarily called habits. These phenomena are of peculiar interest with regard to difficult questions of nutrition and reproduction that perhaps can only be solved by a close study of animals living together in identical conditions and exhibiting, apparently in consequence of so living, similar but by no means identical tendencies, either anatomical or physiological, in certain directions.

One of the most important problems on which the study of the sponges, cœlenterates, and polyzoa of stagnant water throws light is that of the production of resting buds and similar reproductive bodies adapted to withstand unfavourable conditions in a quiescent state and to respond to the renewal of favourable conditions by a renewed growth and activity.

Every autumn, in an English pond or lake, a crisis takes place in the affairs of the less highly organized inhabitants, and preparations are made to withstand the unfavourable conditions due directly or indirectly to the low winter temperature of the water: the individual must perish but the race may be preserved. At this season Hydra, which has been reproducing its kind by means of buds throughout the summer, develops eggs with a hard shell that will lie dormant in the mud until next spring; the phylactolæmatous polyzoa produce statoblasts, the ctenostomatous polyzoa resting-buds ("hibernacula"), and the sponges gemmules. Statoblasts, hibernacula, and gemmules are alike produced asexually, but they resemble the eggs of Hydra in being provided with a hard, resistant shell, and in having the capacity to lie dormant until favourable conditions return.

In an Indian pond or lake a similar crisis takes place in the case of most species, but it does not take place at the same time of year in the case of all species. Unfortunately the phenomena of periodic physiological change have been little studied in the freshwater fauna of most parts of the country, and as yet we know very little indeed of the biology of the Himalayan lakes and tarns, the conditions in which resemble those to be found in similar masses of water in Europe much more closely than they do those that occur in ponds and lakes in a tropical plain. In Bengal, however, I have been able to devote considerable attention to the subject, and can state definitely that some species flourish chiefly in winter and enter the quiescent stage at the beginning of the hot weather (that is to say about March), while others reach their maximum development during the "rains" (July to September) and as a rule die down during winter, which is the driest as well as the coolest time of year.

The following is a list of the forms that in Bengal are definitely known to produce hard-shelled eggs, gemmules, resting-buds, or statoblasts only or most profusely at the approach of the hot weather and to flourish during winter:—

Spongilla carteri.

Sponging alba.

Spongilla alba var. bengalensis.

Spongilla crassissima.

Hydra vulgaris.

Victorella bengalensis.

Plumatella fruticosa.

Plumatella emarginata.

Plumatella javanica.

The following forms flourish mainly during the "rains":—

Spongilla lacustris subsp. reticulata.

Trochospongilla latouchiana.

Trochospongilla phillottiana.

Stolella indica.

The following flourish throughout the year:—

Spongilla proliferens.

Hislopia lacustris.

It is particularly interesting to note that three of the species that flourish in the mild winter of Bengal, namely Hydra vulgaris, Plumatella emarginata, and P. fruticosa, are identical with species that in Europe perish in winter. There is evidence, moreover, that the statoblasts of the genus to which two of them belong burst more readily, and thus give rise to new colonies, after being subjected to a considerable amount of cold. In Bengal they only burst after being subjected to the heat of the hot weather. Does extreme heat have a similar effect on aquatic organisms as extreme cold? There is some evidence that it has.

The species that flourish in India during the rains are all forms which habitually live near the surface or the edge of ponds or puddles, and are therefore liable to undergo desiccation as soon as the rains cease and the cold weather supervenes.

The two species that flourish all the year round do not, properly speaking, belong to one category, for whereas Hislopia lacustris produces no form of resting reproductive body but bears eggs and spermatozoa at all seasons, Spongilla proliferens is a short-lived organism that undergoes a biological crisis every few weeks; that is to say, it begins to develop gemmules as soon as it is fully formed, and apparently dies down as soon as the gemmules have attained maturity. The gemmules apparently lie dormant for some little time, but incessant reproduction is carried on by means of external buds, a very rare method of reproduction among the freshwater sponges.

The facts just stated prove that considerable specific idiosyncrasy exists as regards the biology of the sponges, hydroids, and polyzoa of stagnant water in Bengal; but an even more striking instance of this phenomenon is afforded by the sponges Spongilla bombayensis and Corvospongilla lapidosa in Bombay. These two sponges resemble one another considerably as regards their mode of growth, and are found together on the lower surface of stones. In the month of November, however, C. lapidosa is in full vegetative vigour, while C. bombayensis, in absolutely identical conditions, is already reduced to a mass of gemmules, having flourished during the "rains." It is thus clear that the effect of environment is not identical in different species. This is more evident as regards the groups of animals under consideration in India (and therefore probably in other tropical countries) than it is in Europe. The subject is one well worthy of study elsewhere than in India, for it is significant that specimens of S. bombayensis taken in November in S. Africa were in a state of activity, thus contrasting strongly with specimens taken at the same time of year (though not at the same season from a climatic point of view) in the Bombay Presidency.

Geographical Distribution of the Indian Species.

The geographical distribution of the lower invertebrates of fresh and of stagnant water is often an extremely wide one, probably because the individual of many species exists at certain seasons or in certain circumstances in a form that is not only resistant to unfavourable environment, but also eminently capable of being transported by wind or currents. We therefore find that some genera and even species are practically cosmopolitan in their range, while others, so far as our knowledge goes, appear to have an extraordinarily discontinuous distribution. The latter phenomenon may be due solely to our ignorance of the occurrence of obscure genera or species in localities in which they have not been properly sought for, or it may have some real significance as indicating that certain forms cannot always increase and multiply even in those localities that appear most suitable for them. As an example of universally distributed species we may take the European polyzoa of the genus Plumatella that occur in India, while of species whose range is apparently discontinuous better examples could not be found than the sponges Trochospongilla pennsylvanica and Spongilla crateriformis, both of which are only known from N. America, the British Isles, and India.

My geographical list of the species of sponges, cœlenterates, and polyzoa as yet found in fresh water in India is modelled on Col. Alcock's recently published list of the freshwater crabs (Potamonidæ) of the Indian Empire[^[B]]. I follow him in accepting, with slight modifications of my own, Blanford's physiographical rather than his zoogeographical regions, not because I think that the latter have been or ought to be superseded so far as the vertebrates are concerned, but rather because the limits of the geographical distribution of aquatic invertebrates appear to depend on different factors from those that affect terrestrial animals or even aquatic vertebrates.

"Varieties" are ignored in this list, because they are not considered to have a geographical significance. The parts of India that are least known as regards the freshwater representatives of the groups under consideration are the valley of the Indus, the lakes of Kashmir and other parts of the Himalayas, the centre of the Peninsula, and the basin of the Brahmaputra. Those that are best known are the districts round Bombay, Calcutta, Madras and Bangalore, Travancore and Northern Tenasserim. Little is known as regards Ceylon, and almost nothing as regards the countries that surround the Indian Empire, a few species only having been recorded from Yunnan and the Malay Peninsula, none from Persia, Afghanistan, or Eastern Turkestan, and only one from Tibet. Professor Max Weber's researches have, however, taught us something as regards Sumatra and Java, while the results of various expeditions to Tropical Africa are beginning to cast light on the lower invertebrates of the great lakes in the centre of that continent and of the basin of the Nile.

It is not known to what altitude the three groups range in the Himalayas and the hills of Southern India. No sponge has been found in Indian territory at an altitude higher than that of Bhim Tal in Kumaon (4,500 feet), and Hydra is only known from the plains; but a variety of H. oligactis was taken by Capt. F. H. Stewart in Tibet at an altitude of about 15,000 feet. Plumatella diffusa flourishes at Gangtok in Sikhim (6,100 feet), and I have found statoblasts of P. fruticosa in the neighbourhood of Simla on the surface of a pond situated at an altitude of about 8,000 feet; Mr. R. Kirkpatrick obtained specimens of the genus in the Botanical Gardens at Darjiling (6,900 feet), and two species have been found at Kurseong (4,500-5,000 feet) in the same district.

GEOGRAPHICAL LIST OF THE FRESHWATER SPONGES, HYDROIDS, AND POLYZOA OF INDIA, BURMA, AND CEYLON.

[A * indicates that a species or subspecies has only been found in one physiographical region or subregion so far as the Indian Empire is concerned; a † that the species has also been found in Europe, a § in North America, a ✻ in Africa, and a ʘ in the Malay Archipelago.]

1. Western Frontier Territory[^[C]].

(Baluchistan, the Punjab, and the N.W. Frontier Province.)

Sponges:—

1. Spongilla (Eunapius) carteri†ʘ (Lahore).

Hydroids:—

1. Hydra oligactis†§ (Lahore).

Polyzoa:—

1. Plumatella fruticosa†§ (Lahore).

2. Plumatella diffusa†§ (Lahore).

2. Western Himalayan Territory.

(Himalayas from Hazara eastwards as far as Nepal.)

Sponges:—

1. Spongilla (Eunapius) carteri†ʘ (Bhim Tal).

2. Ephydatia meyeniʘ (Bhim Tal).

Hydroids:—None known (Hydra oligactis recorded from Tibet).

Polyzoa:—

1. Plumatella allmani† (Bhim Tal).

2. Plumatella fruticosa†§ (Simla).

3. Lophopodella carteri✻ (Bhim Tal).

3. North-Eastern Frontier Territory.

(Sikhim, Darjiling and Bhutan, and the Lower Brahmaputra Drainage-System.)

Sponges:—

Spongilla proliferensʘ (Assam).

Hydroids:—None known.

Polyzoa:—

1. Plumatella fruticosa† (Kurseong and Assam).

2. Plumatella diffusa†§ (Sikhim).

3. Plumatella javanicaʘ (Kurseong).

4. Burma Territory.

(Upper Burma, Arrakan, Pegu, Tenasserim.)

Sponges:—

1. Spongilla (Euspongilla) proliferensʘ (Upper Burma, Pegu).

2. Spongilla (Euspongilla) crateriformis†§ (Tenasserim).

3. Spongilla (Eunapius) carteri†ʘ (Upper Burma, Pegu, Tenasserim).

4. Trochospongilla latouchiana (Tenasserim).

5. Trochospongilla phillottiana (Tenasserim).

6. Tubella vesparioides* (Tenasserim).

7. Corvospongilla burmanica* (Pegu).

Hydroids:—

1. Hydra vulgaris†§ (Upper Burma and Tenasserim).

Polyzoa:—

1. Plumatella emarginata†§ (Pegu, Upper Burma).

2. Plumatella allmani† (Tenasserim).

3. Pectinatella burmanica (Tenasserim).

4. Hislopia lacustris (Pegu).

5 a. Peninsular Province—Main Area.

(The Peninsula east of the Western Ghats.)

Sponges:—

1. Spongilla (Euspongilla) lacustris subsp. reticulata (Orissa, Madras).

2. Spongilla (Euspongilla) proliferensʘ (Madras).

3. Spongilla (Euspongilla) alba✻ (N. Madras, Orissa, Hyderabad).

4. Spongilla (Euspongilla) hemephydatia* (Orissa).

5. Spongilla (Euspongilla) crateriformis†§.

6. Spongilla (Eunapius) carteri†ʘ.

7. Spongilla (Eunapius) gemina* (Bangalore).

8. Spongilla (Stratospongilla) bombayensis✻ (Mysore).

9. Dosilia plumosa (N. Madras).

Hydroids:—

1. Hydra vulgaris†§.

Polyzoa:—

1. Plumatella fruticosa† (Madras, Bangalore).

2. Lophopus (?Lophopodella), sp. (Madras).

3. Pectinatella burmanica (Orissa).

4. Victorella bengalensis (Madras).

5. Hislopia lacustris (Nagpur).

5b. Peninsular Province—Malabar Zone.

(Western Ghats from Tapti R. to Cape Comorin and eastwards to the sea.)

Sponges:—

1. Spongilla (Euspongilla) lacustris subsp. reticulata (W. Ghats).

2. Spongilla (Euspongilla) proliferensʘ (Cochin).

3. Spongilla (Euspongilla) alba✻.

4. Spongilla (Euspongilla) cinerea*.

5. Spongilla (Euspongilla) travancorica* (Travancore).

6. Spongilla (Euspongilla) crateriformis†§ (Cochin).

7. Spongilla (Eunapius) carteri†ʘ.

8. Spongilla (Stratospongilla) indica* (W. Ghats).

9. Spongilla (Stratospongilla) bombayensis✻ (Bombay, W. Ghats).

10. Spongilla (Stratospongilla) ultima* (Travancore).

11. Pectispongilla aurea* (Travancore, Cochin).

12. Ephydatia meyeniʘ (Bombay, Travancore).

13. Dosilia plumosa (Bombay).

14. Trochospongilla pennsylvanica*†§ (Travancore).

15. Corvospongilla lapidosa* (W. Ghats).

Hydroids:—None recorded.

Polyzoa:—

1. Fredericella indica* (W. Ghats and Travancore).

2. Plumatella fruticosa† (Bombay).

3. Plumatella javanicaʘ (Travancore).

4. Plumatella tanganyikæ*✻ (W. Ghats).

5. Lophopodella carteri✻ (Bombay, W. Ghats).

6. Indo-Gangetic Plain.

(From Sind to the Brahmaputra.)

Sponges:—

1. Spongilla (Euspongilla) lacustris subsp. reticulata (Gangetic delta).

2. Spongilla (Euspongilla) proliferensʘ (Lower Bengal, etc.).

3. Spongilla (Euspongilla) alba✻ (Lower Bengal).

4. Spongilla (Euspongilla) crateriformis†§.

5. Spongilla (Eunapius) carteri†ʘ (Lower Bengal, etc.).

6. Spongilla (Eunapius) fragilis subsp. calcuttana* (Lower Bengal).

7. Spongilla (Eunapius) crassissima (Bengal).

8. Ephydatia meyeniʘ (Lower Bengal).

9. Trochospongilla latouchiana (Lower Bengal).

10. Trochospongilla phillottiana (Lower Bengal).

Hydroids:—

1. Hydra vulgaris†§.

Polyzoa:—

1. Plumatella fruticosa†.

2. Plumatella emarginata†§.

3. Plumatella javanicaʘ (Lower Bengal).

4. Plumatella diffusa†§.

5. Plumatella allmani†.

6. Plumatella punctata†§ (Lower Bengal).

7. Stolella indica* (Lower Bengal, United Provinces).

8. Victorella bengalensis (Lower Bengal).

9. Hislopia lacustris (United Provinces, N. Bengal).

9a. Hislopia lacustris subsp. moniliformis* (Lower Bengal).

7. Ceylon.

Sponges:—

1. Spongilla (Euspongilla) proliferensʘ.

2. Spongilla (Eunapius) carteri†ʘ.

Hydroids:—

1. Hydra vulgaris†§.

Polyzoa:—

1. ? Plumatella emarginata†§.

2. Pectinatella burmanica.

The most striking feature of this list is the evidence it affords as to the distinct character of the fauna of the Malabar Zone, a feature that is also remarkably clear as regards the Potamonidæ, one genus of which (Gecarcinucus) is peculiar, so far as India is concerned, to that zone. As regards the sponges we may note the occurrence of no less than three species of the subgenus Stratospongilla, which has not been found elsewhere in India except on one occasion in Mysore, and of a species of the genus Corvospongilla, which is unknown from the rest of Peninsular India and from the Himalayas. The genus Pectispongilla is only known from the Malabar Zone. Among the polyzoa the genus Fredericella[^[D]] appears to be confined, so far as the Indian and Burmese fauna is concerned, to the Malabar Zone, and the same is true as regards the group of species to which Plumatella tanganyikæ, an African form, belongs.

A further examination of the list of Malabar species and a consideration of allied forms shows that the majority of the forms restricted to the Malabar Zone are either African or else closely allied to African forms. The genus Corvospongilla, except for one Burmese species, is otherwise peculiar to Tropical Africa; while Stratospongilla, although not confined to Africa, is more prolific in species in that continent than in any other. Spongilla (Stratospongilla) bombayensis has only been found in Bombay, the Western Ghats, Mysore, and Natal, and Plumatella tanganyikæ only in the Western Ghats and Central Africa. The genus Fredericella (which also occurs in Europe, N. America, and Australia) is apparently of wide distribution in Africa, while Lophopodella (which in India is not confined to the Malabar Zone) is, except for a Japanese race of the Indian species, restricted outside India, so far as we know, to East Africa.

A less definite relationship between the sponges and polyzoa of the Malabar Zone and those of countries to the east of India is suggested by the following facts:—

(1) The occurrence of the genus Corvospongilla in Burma;
(2) the occurrence of the subgenus Stratospongilla in Sumatra, China, and the Philippines;
(3) the occurrence of a race of Lophopodella carteri in Japan;
(4) the occurrence of a species allied to Plumatella tanganyikæ in the Philippines.

It will be noted that in each of these instances the relationship extends to Africa as well as to the Eastern countries, and is more marked in the former direction. The species of Stratospongilla, moreover, that occurs in Sumatra (S. sumatrensis) also occurs in Africa, while those that have been found in China and the Philippines are aberrant forms.

At first sight it might appear that these extra-Indian relationships might be explained by supposing that gemmules and statoblasts were brought to the Malabar Coast from Africa by the aërial currents of the monsoon or by marine currents and carried from India eastwards by the same agency, this agency being insufficient to transport them to the interior and the eastern parts of the Peninsula. The work of La Touche[^[E]] on wind-borne foraminifera in Rajputana is very suggestive in this direction; but that the peculiar sponge and polyzoon fauna of Malabar is due to the agency either of wind or of marine currents may be denied with confidence, for it is a striking fact that most of the characteristic genera and subgenera of the Zone have resting reproductive bodies that are either fixed to solid objects or else are devoid of special apparatus to render them light. The former is the case as regards all species of Corvospongilla and all Indian and most other species of Stratospongilla, the gemmules of which not only are unusually heavy but also adhere firmly; while the statoblasts of Fredericella have no trace of the air-cells that render the free statoblasts of all other genera of phylactolæmatous polyzoa peculiarly light and therefore peculiarly liable to be transported by wind.

A true geographical or geological explanation must therefore be sought for the relationship between the sponges and polyzoa of Malabar, of Africa, and of the Eastern countries—a relationship that is well known to exist as regards other groups of animals. No more satisfactory explanation has as yet been put forward than that of a former land connection between Africa and the Malaysia through Malabar at a period (probably late Cretaceous) when the Western Ghats were much higher than they now are[^[F]].

There is little to be said as regards the distribution of the sponges, hydroids, and polyzoa of fresh water in other parts of India. It may be noted, however, that the species known from the Punjab are all widely distributed Palæarctic forms, and that the genus Stolella is apparently confined to the Indo-Gangetic Plain. Two species of sponge are peculiar to Lower Burma, one of them (Corvospongilla burmanica) representing the geographical alliance already discussed as regards the Malabar Zone, the other (Tubella vesparioides) closely related to a Malaysian species (T. vesparium from Borneo) and perhaps representing the northern limit of the Malaysian element well known in the fauna of Lower Burma. Of the sponges and polyzoa of Ceylon we know as yet too little to make it profitable to discuss their affinities. All that have as yet been discovered occur also in Peninsular India; nor do they afford any evidence of a connection with the Malabar Zone.

The question of the geographical range of the sponges, hydroids, and polyzoa of brackish water may be considered briefly, for it is of importance in considering that of those which are confined to fresh water. Some of these species from brackish water (e. g., Membranipora lacroixii) are identical with others (e. g., Victorella bengalensis and Bowerbankia caudata subsp. bengalensis) closely related to European forms. Others again (e. g., Loxosomatoides colonialis and Sagartia schilleriana) are known as yet from the Ganges delta only. In our ignorance of the Indian representatives of the groups to which they belong, it is impossible to assert that their distribution is actually so restricted as it seems.

Some Special Localities.

In order to avoid constant repetition as regards the conditions that prevail at the places most frequently mentioned in this volume, a few details as regards them may be conveniently stated here.

Lower Bengal.

Calcutta is situated on the River Hughli at a point about 90 miles from the open sea. The water of the river is practically fresh, but is strongly affected by the tides; it is always turbid and of a brownish colour. The river, however, is not a good collecting ground for sponges, cœlenterates, and polyzoa, and none of the species described in this volume have been obtained from it. It is in the Calcutta "tanks" that most of my investigations have been made. These tanks are ponds, mostly of artificial origin, very numerous, of varying size but never very large or deep. Most of them contain few solid objects to which sedentary organisms can fix themselves, and such ponds are of course poor in sponges and polyzoa. Others, however, support a prolific growth of weeds such as Pistia stratiotes, Lemna, and Limnanthemum, and a few have brickwork or artificial stonework at their sides. In those parts of the town that approach the Salt Lakes (large lagoons and swamps of brackish water connected with the sea by the Mutlah River) the water of the ponds is slightly brackish and permits few plants except algæ to flourish. Few of the bigger tanks ever dry up. The best of the tanks from the sponge-collector's point of view, so far as I have been able to discover, is the one in the compound of the Indian Museum. It enjoys all the advantages of light and shade, solid supports, prolific aquatic vegetation, considerable depth, and the vicinity of human dwellings that seem to be favourable to the growth of sponges, no less than nine species of which, representing three genera and two subgenera, grow abundantly in it. Hydra also flourishes in this pond, but for some reasons there are few polyzoa. The phylactolæmatous species of the latter group, however, are extraordinarily abundant in one of the tanks in the Zoological Gardens at Alipore. In this tank, which unlike the Museum tank is directly connected with the river, no less than six species and varieties of the genus Plumatella have been found growing together on sticks, floating seeds, and water-plants. Except Hislopia, which is common on Vallisneria in one tank on the Maidan (opposite the Bengal Club), the ctenostomes of stagnant water are only found in the tanks near the Salt Lakes.

Port Canning is situated on the Mutlah River about 30 miles from Calcutta and about 60 from the open sea. The Mutlah is really a tidal creek rather than a river, in spite of the fact that it runs for a considerable number of miles, and its waters are distinctly brackish. Water taken from the edge at Port Canning in March was found to contain 25.46 per thousand of saline residue. The interesting feature of Port Canning, however, is from a zoological point of view not the Mutlah but certain ponds of brackish water now completely separated from it, except occasionally when the river is in flood, but communicating regularly with it in the memory of living persons. These ponds, which were apparently not in existence in 1855, have on an average an area of about half an acre each, and were evidently formed by the excavation of earth for the construction of an embankment along the Mutlah. They are very shallow and lie exposed to the sun. The salinity differs considerably in different ponds, although the fauna seems to be identical; the water of one pond was found to contain 22.88 per thousand of saline residue in May, 20.22 per thousand in March, and 12.13 in December. A second pond in the neighbourhood of the first and apparently similar to it in every way contained only 9.82 per thousand in July, after the rains had broken. The fauna of these ponds includes not only a freshwater sponge (Spongilla alba var. bengalensis) but also many aquatic insects (e. g., larvæ of mosquitos and of Chironomus and several species of beetles and Rhynchota); while on the other hand essentially marine cœlenterates (Irene ceylonensis, etc.) and worms (e. g., the gephyrean Physcosoma lurco[^[G]]) form a part of it, together with forms of intermediate habitat such as Bowerbankia caudata subsp. bengalensis, Victorella bengalensis, and several fish and crustacea common in brackish water.

Orissa.

Orissa may be described in general terms as consisting of the coastal area of Bengal south of the Gangetic delta. It extends in inland, however, for a considerable distance and includes hilly tracts. There is no geographical boundary between it and the north-eastern part of the Madras Presidency or the eastern part of the Central Provinces.

Chilka Lake.—This marine lake is a shallow lagoon measuring about 40 miles in length and 10 miles in breadth, and formed in geologically recent times by the growth of a narrow sand-bank across the mouth of a wide bay. At its northern end it communicates with the sea by a narrow channel, and throughout its length it is strongly affected by the tides. At its south end, which is actually situated in the Ganjam district of Madras, the water is distinctly brackish and is said to be nearly fresh at certain times of year. At this end there are numerous small artificial pools of brackish water somewhat resembling those of Port Canning as regards their fauna.

Sur (or Sar) Lake.—A shallow, freshwater lake of very variable size situated a few miles north of Puri on the Orissa coast. In origin it probably resembled the Chilka Lake, but it is now separated from the sea by about 3 miles of barren sand dunes, among which numerous little pools of rain-water are formed during the rains. These dry up completely in winter, and even the lake itself is said sometimes almost to disappear, although when it is full it is several miles in length. The fauna is essentially a freshwater one, but includes certain Mysidæ and other crustacea usually found in brackish water.

Bombay Presidency.

Bombay.—The town of Bombay, built on an island near the mainland, is situated close to swamps and creeks of brackish water not unlike those that surround Calcutta. Its "tanks," however, differ from those of Calcutta in having rocky bottoms and, in many cases, in drying up completely in the hot weather. Of the fauna of the swamps extremely little is known, but so far as the sponges and polyzoa of the tanks are concerned the work undertaken by Carter was probably exhaustive.

Igatpuri.—Igatpuri is situated at an altitude of about 2000 feet, 60 miles north-east of Bombay. Above the town there is a lake of several square miles in area whence the water-supply of several stations in the neighbourhood is obtained. The water is therefore kept free from contamination. The bottom is composed of small stones and slopes gradually up at the edges. During the dry weather its level sinks considerably. Several interesting sponges and polyzoa have been found in this lake, most of them also occurring in a small pond in the neighbourhood in which clothes are washed and the water is often full of soap-suds.

Southern India.

Madras.—The city of Madras is built by the sea, straggling over a large area of the sandy soil characteristic of the greater part of the east coast of India. In wet weather this soil retains many temporary pools of rain-water, and there are numerous permanent tanks of no great size in the neighbourhood of the town. The so-called Cooum River, which flows through the town, is little more than a tidal creek, resembling the Mutlah River of Lower Bengal on a much smaller scale. The sponges and polyzoa as yet found in the environs of Madras are identical with those found in the environs of Calcutta.

Bangalore.—Bangalore (Mysore State) is situated near the centre of the Madras Presidency on a plateau about 3000 feet above sea-level. The surrounding country is formed of laterite rock which decomposes readily and forms a fine reddish silt in the tanks. These tanks are numerous, often of large size, and as a rule at least partly of artificial origin. Their water supports few phanerogamic plants and is, as my friend Dr. Morris Travers informs me, remarkably free from salts in solution. The sponge fauna of the neighbourhood of Bangalore appears to be intermediate between that of Madras and that of Travancore.

The Backwaters of Cochin and Travancore.—The "backwaters" of Cochin and Travancore were originally a series of shallow lagoons stretching along the coast of the southern part of the west coast of India for a distance of considerably over a hundred miles. They have now been joined together by means of canals and tunnels to form a tidal waterway, which communicates at many points directly with the sea. The salinity of the water differs greatly at different places and in different seasons, and at some places there is an arrangement to keep out sea-water while the rice-fields are being irrigated. The fauna is mainly marine, but in the less saline parts of the canals and lakes many freshwater species are found.

Shasthancottah.—There are two villages of this name, one situated on the backwater near Quilon (coast of Travancore), the other about three miles inland on a large freshwater lake. This lake, which does not communicate with the backwater, occupies a narrow winding rift several miles in length at a considerable depth below the surrounding country. Its bottom is muddy and it contains few water-plants, although in some places the water-plants that do exist are matted together to form floating islands on which trees and bushes grow. The fauna, at any rate as regards mollusca and microscopic organisms, is remarkably poor, but two species of polyzoa (Fredericella indica and Plumatella fruticosa) and one of sponge (Trochospongilla pennsylvanica) grow in considerable abundance although not in great luxuriance.

The Himalayas.

Bhim Tal[^[H]] is a lake situated at an altitude of 4500 feet in that part of the Western Himalayas known as Kumaon, near the plains. It has a superficial area of several square miles, and is deep in the middle. Its bottom and banks are for the most part muddy. Little is known of its fauna, but two polyzoa (Plumatella allmani and Lophopodella carteri) and the gemmules of two sponges (Spongilla carteri and Ephydatia meyeni) have been found in it.

* * * * *

Nomenclature and Terminology.

The subject of nomenclature may be considered under four heads:—(I.) the general terminology of the various kinds of groups of individuals into which organisms must be divided; (II.) the general nomenclature of specimens belonging to particular categories, such as types, co-types, etc.; (III.) the nomenclature that depends on such questions as that of "priority"; and (IV.) the special terminology peculiar to the different groups. The special terminology peculiar to the different groups is dealt with in the separate introductions to each of the three parts of this volume.

(I.)

No group of animals offers greater difficulty than the sponges, hydroids, and polyzoa (and especially the freshwater representatives of these three groups) as regards the question "What is a species?" and the kindred questions, "What is a subspecies?" "What is a variety?" and "What is a phase?" Genera can often be left to look after themselves, but the specific and kindred questions are answered in so many different ways, if they are even considered, by different systematists, especially as regards the groups described in this volume, that I feel it necessary to state concisely my own answers to these questions, not for the guidance of other zoologists but merely to render intelligible the system of classification here adopted. The following definitions should therefore be considered in estimating the value of "species," etc., referred to in the following pages.

Species.—A group of individuals differing in constant characters of a definite nature and of systematic[^[I]] importance from all others in the same genus.

Subspecies.—An isolated or local race, the individuals of which differ from others included in the same species in characters that are constant but either somewhat indefinite or else of little systematic importance.

Variety.—A group of individuals not isolated geographically from others of the same species but nevertheless exhibiting slight, not altogether constant, or indefinite differences from the typical form of the species (i. e., the form first described).

Phase.—A peculiar form assumed by the individuals of a species which are exposed to peculiarities in environment and differ from normal individuals as a direct result.

There are cases in which imperfection of information renders it difficult or impossible to distinguish between a variety and a subspecies. In such cases it is best to call the form a variety, for this term does not imply any special knowledge as regards its distribution or the conditions in which it is found.

I use the term "form" in a general sense of which the meaning or meanings are clear without explanation.

(II.)

The question of type specimens must be considered briefly. There are two schools of systematists, those who assert that one specimen and one only must be the type of a species, and those who are willing to accept several specimens as types. From the theoretical point of view it seems impossible to set up any one individual as the ideal type of a species, but those who possess collections or are in charge of museums prefer, with the natural instinct of the collector, to have a definite single type (of which no one else can possibly possess a duplicate) in their possession or care, and there is always the difficulty that a zoologist in describing a species, if he recognizes more than one type, may include as types specimens that really belong to more than one species. These difficulties are met by some zoologists by the recognition of several specimens as paratypes, all of equal value; but this, after all, is merely a terminological means of escaping from the difficulty, calculated to salve the conscience of a collector who feels unwilling to give up the unique type of a species represented by other specimens in his collection. The difficulty as regards the confounding of specimens of two or more species as the types of one can always be adjusted if the author who discovers the mistake redescribes one of the species under the original name and regards the specimen that agrees with his description as the type, at the same time describing a new species with another of the specimens as its type. Personally I always desire to regard the whole material that forms the basis of an original description of a species as the type, but museum rules often render this impossible, and the best that can be done is to pick out one specimen that seems particularly characteristic and to call it the type, the rest of the material being termed co-types. A peculiar difficulty arises, however, as regards many of the sponges, cœlenterates, and polyzoa, owing to the fact that they are often either compound animals, each specimen consisting of more than one individual, or are easily divisible into equivalent fragments. If the single type theory were driven to its logical conclusion, it would be necessary to select one particular polyp in a hydroid colony, or even the part of a sponge that surrounded a particular osculum as the type of the species to which the hydroid or the sponge belonged. Either by accident or by design specimens of Spongillidæ, especially if kept dry, are usually broken into several pieces. There is, as a matter of fact, no reason to attribute the peculiarly sacrosanct nature of a type to one piece more than another. In such cases the biggest piece may be called the type, while the smaller pieces may be designated by the term "schizotype."

The more precise definition of such terms as topotype, genotype, et hujus generis omnis is nowadays a science (or at any rate a form of technical industry) by itself and need not be discussed here.

(III.)

In 1908 an influential committee of British zoologists drew up a strenuous protest against the unearthing of obsolete zoological names (see 'Nature,' Aug. 1908, p. 395). To no group does this protest apply with greater force than to the three discussed in this volume. It is difficult, however, to adopt any one work as a standard of nomenclature for the whole of any one of them. As regards the Spongillidæ it is impossible to accept any monograph earlier than Potts's "Fresh-Water Sponges" (P. Ac. Philad., 1887), for Bowerbank's and Carter's earlier monographs contained descriptions of comparatively few species. Even Potts's monograph I have been unable to follow without divergence, for it seems to me necessary to recognize several genera and subgenera that he ignored. The freshwater polyzoa, however, were dealt with in so comprehensive a manner by Allman in his "Fresh-Water Polyzoa" (London, 1856) that no difficulty is experienced in ignoring, so far as nomenclature is concerned, any earlier work on the group; while as regards other divisions of the polyzoa I have followed Hincks's "British Marine Polyzoa" (1880), so far as recent researches permit. In most cases I have not attempted to work out an elaborate synonymy of species described earlier than the publication of the works just cited, for to do so is a mere waste of time in the case of animals that call for a most precise definition of species and genera and yet were often described, so far as they were known earlier than the dates in question, in quite general terms. I have been confirmed in adopting this course by the fact that few of the types of the earlier species are now in existence, and that a large proportion of the Indian forms have only been described within the last few years.

Material.

The descriptions in this volume are based on specimens in the collection of the Indian Museum, the Trustees of which, by the liberal manner in which they have permitted me to travel in India and Burma on behalf of the Museum, have made it possible not only to obtain material for study and exchange but also to observe the different species in their natural environment. This does not mean to say that specimens from other collections have been ignored, for many institutions and individuals have met us generously in the matter of gifts and exchanges, and our collection now includes specimens of all the Indian forms, named in nearly all cases by the author of the species, except in those of species described long ago of which no authentic original specimens can now be traced. Pieces of the types of all of the Indian Spongillidæ described by Carter have been obtained from the British Museum through the kind offices of Mr. R. Kirkpatrick. The Smithsonian Institution has sent us from the collection of the United States National Museum specimens named by Potts, and the Berlin Museum specimens named by Weltner, while to the Imperial Academy of Sciences of St. Petersburg we owe many unnamed but interesting sponges. Dr. K. Kraepelin and Dr. W. Michaelsen have presented us with specimens of most of the species and varieties of freshwater polyzoa described by the former in his great monograph and elsewhere. We owe to Dr. S. F. Harmer, formerly of the Cambridge University Museum and now Keeper in Zoology at the British Museum, to Professor Max Weber of Amsterdam, Professor Oka of Tokyo, and several other zoologists much valuable material. I would specially mention the exquisite preparations presented by Mr. C. Rousselet. Several naturalists in India have also done good service to the Museum by presenting specimens of the three groups described in this volume, especially Major H. J. Walton, I.M.S., Major J. Stephenson, I.M.S., Dr. J. R. Henderson and Mr. G. Matthai of Madras, and Mr. R. Shunkara Narayana Pillay of Trivandrum.

The following list shows where the types of the various species, subspecies, and varieties are preserved, so far as it has been possible to trace them. I have included in this list the names of all species that have been found in stagnant water, whether fresh or brackish, but those of species not yet found in fresh water are enclosed in square brackets.

The literature dealing with the various groups described in the volume is discussed in the introductions to the three parts. Throughout the volume I have, so far as possible, referred to works that can be consulted in Calcutta in the libraries of the Indian Museum, the Geological Survey of India, or the Asiatic Society of Bengal. The names of works that are not to be found in India are marked with a *. The rarity with which this mark occurs says much for the fortunate position in which zoologists stationed in Calcutta find themselves as regards zoological literature, for I do not think that anything essential has been omitted.

It remains for me to express my gratitude to those who have assisted me in the preparation of this volume. The names of those who have contributed specimens for examination have already been mentioned. I have to thank the Trustees of the Indian Museum not only for their liberal interpretation of my duties as an officer of the Museum but also for the use of all the drawings and photographs and some of the blocks from which this volume is illustrated. Several of the latter have already been used in the "Records of the Indian Museum." From the Editor of the "Fauna" I have received valuable suggestions, and I am indebted to Dr. Weltner of the Berlin Museum for no less valuable references to literature. Mr. F. H. Gravely, Assistant Superintendent in the Indian Museum, has saved me from several errors by his criticism.

The majority of the figures have been drawn by the draftsmen of the Indian Museum, Babu Abhoya Charan Chowdhary, and of the Marine Survey of India, Babu Shib Chandra Mondul, to both of whom I am much indebted for their accuracy of delineation.

No work dealing with the sponges of India would be complete without a tribute to the memory of H. J. Carter, pioneer in the East of the study of lower invertebrates, whose work persists as a guide and an encouragement to all of us who are of the opinion that biological research on Indian animals can only be undertaken in India, and that even systematic zoological work can be carried out in that country with success. I can only hope that this, the first volume in the official Fauna of the Indian Empire to be written entirely in India, may prove not unworthy of his example.

Indian Museum, Calcutta Oct. 23rd, 1910.

[A] "L'origine des animaux d'eau douce," Bull. de l'Acad. roy. de Belgique (Classe des Sciences), No. 12, 1905, p. 724.

[B] Cat. Ind. Dec. Crust. Coll. Ind. Mus., part i, fasc. ii (Potamonidæ), 1910.

[C] I include Baluchistan in this territory largely for climatic reasons.

[D] Mr. S. W. Kemp recently obtained at Mangaldai, near the Bhutan frontier of Assam, a single specimen of what may be a species of Fredericella.

[E] See Mem. Geol. Surv. Ind. xxxv (1), p. 39 (1902).

[F] See Ortmann, "The Geographical Distribution of Freshwater Decapods and its bearing upon Ancient Geography," Proc. Amer. Phil. Soc. xli, p. 380, fig. 6 (1902); also Suess, "The Face of the Earth" (English ed.) i, p. 416 (1904).

[G] I am indebted to Mr. W. F. Lanchester for the identification of this species.

[H] The fauna of this lake and of others in the neighbourhood has recently been investigated by Mr. S. W. Kemp. See the addenda at the end of this volume.—June 1911.

[I] "What characters are of systematic importance?" is a question to which different answers must be given in the case of different groups.

[J] I have failed to obtain from the Philadelphia Academy of Science a statement that the type of this species is still in existence.

PART I.
FRESHWATER SPONGES
(SPONGILLIDÆ).

INTRODUCTION TO PART I.

I.

The Phylum Porifera.

The phylum Porifera or Spongiæ includes the simplest of the Metazoa or multicellular animals. From the compound Protozoa its members are distinguished by the fact that the cells of which they are composed exhibit considerable differentiation both in structure and in function, and are associated together in a definite manner, although they are not combined to form organs and systems of organs as in the higher Metazoa. Digestion, for instance, is performed in the sponges entirely by individual cells, into the substance of which the food is taken, and the products of digestion are handed on to other cells without the intervention of an alimentary canal or a vascular system, while there is no structure in any way comparable to the nervous system of more highly organized animals.

The simplest form of sponge, which is known as an olynthus, is a hollow vase-like body fixed at one end to some solid object, and with an opening called the osculum at the other. The walls are perforated by small holes, the pores, from which the name Porifera is derived.

Externally the surface is protected by a delicate membrane formed of flattened cells and pierced by the pores, while the interior of the vase is covered with curious cells characteristic of the sponges, and known as choanocytes or collar-cells. They consist of minute oval or pear-shaped bodies, one end of which is provided with a rim or collar of apparently structureless membrane, while a flagellum or whip-like lash projects from the centre of the surface surrounded by the collar. These collar-cells are practically identical with those of which the Protozoa known as Choanoflagellata consist; but it is only in the sponges[^[K]] that they are found constantly associated with other cells unlike themselves.

In addition to the collar-cells, which form what is called the gastral layer, and the external membrane (the derma or dermal membrane), the sponge contains cells of various kinds embedded in a structureless gelatinous substance, through which they have the power of free movement. Most of these cells have also the power of changing their form in an "amœboid" manner; that is to say, by projecting and withdrawing from their margin mobile processes of a more or less finger-like form, but unstable in shape or direction. The protoplasm of which some of the cells are formed is granular, while that of others is clear and translucent. Some cells, which (for the time being at any rate) do not exhibit amœboid movements, are glandular in function, while others again give rise in various ways to the bodies by means of which the sponge reproduces its kind. There is evidence, however, that any one kind of cell, even those of the membrane and the gastral layer, can change its function and its form in case of necessity.

Most sponges possess a supporting framework or skeleton. In some it is formed entirely of a horny substance called spongin (as in the bath-sponge), in others it consists of spicules of inorganic matter (either calcareous or siliceous) secreted by special cells, or of such spicules bound together by spongin. Extraneous objects, such as sand-grains, are frequently included in the skeleton. The spongin is secreted like the spicules by special cells, but its chemical structure is much more complicated than that of the spicules, and it is not secreted (at any rate in most cases) in such a way as to form bodies of a definite shape. In the so-called horny sponges it resembles the chitin in which insects and other arthropods are clothed.

* * * * *

In no adult sponge do the collar-cells completely cover the whole of the internal surface, the olynthus being a larval form, and by no means a common larval form. It is only found in certain sponges with calcareous spicules. As the structure of the sponge becomes more complicated the collar-cells are tucked away into special pockets or chambers known as ciliated chambers, and finally the approach to these chambers, both from the external surface and from the inner or gastral cavity, takes the form of narrow tubes or canals instead of mere pores. With further complexity the simple internal cavity tends to disappear, and the sponge proliferates in such a way that more than one osculum is formed. In the class Demospongiæ, to which the sponges described in this volume belong, the whole system is extremely complicated.

The skeleton of sponges, when it is not composed wholly of spongin, consists of, or at any rate contains, spicules that have a definite chemical composition and definite shapes in accordance with the class, order, family, genus, and species of the sponge. Formerly sponges were separated into calcareous, siliceous, and horny sponges by the nature of their skeleton; and although the system of classification now adopted has developed into a much more complex one and a few sponges are known that have both calcareous and siliceous spicules, the question whether the spicules are formed of salts of lime or of silica (strictly speaking of opal) is very important. All Demospongiæ that have spicules at all have them of the latter substance, and the grade Monaxonida, in which the freshwater sponges constitute the family Spongillidæ, is characterized by the possession of spicules that have typically the form of a needle pointed at both ends. Although spicules of this simple form may be absent in species that belong to the grade, the larger spicules, which are called megascleres, have not normally more than one main axis and are always more or less rod-like in outline. They are usually arranged so as to form a reticulate skeleton. Frequently, however, the megascleres or skeleton-spicules are not the only spicules present, for we find smaller spicules (microscleres) of one or more kinds lying loose in the substance of the sponge and in the external membrane, or, in the Spongillidæ only, forming a special armature for the reproductive bodies known as gemmules.

All sponges obtain their food in the same way, namely by means of the currents of water set up by the flagella of the collar-cells. These flagella, although apparently there is little concerted action among them, cause by their rapid movements changes of pressure in the water contained in the cavities of the sponge. The water from outside therefore flows in at the pores and finally makes its way out of the oscula. With the water minute particles of organic matter are brought into the sponge, the collar-cells of which, and probably other cells, have the power of selecting and engulfing suitable particles. Inside the cells these particles undergo certain chemical changes, and are at least partially digested. The resulting substances are then handed on directly to other cells, or, as some assert, are discharged into the common jelly, whence they are taken up by other cells.

Sponges reproduce their kind in more ways than one, viz., by means of eggs (which are fertilized as in other animals by spermatozoa), by means of buds, and by means of the peculiar bodies called gemmules the structure and origin of which is discussed below (p. 42). They are of great importance in the classification of the Spongillidæ. Sponges can also be propagated artificially by means of fission, and it is probable that this method of reproduction occurs accidentally, if not normally, in natural circumstances.

General Structure of the Spongillidæ.

It would be impracticable in this introduction to give a full account of the structure of the Spongillidæ, which in some respects is still imperfectly known. Students who desire further information should consult Professor Minchin's account of the sponges in Lankester's 'Treatise on Zoology,' part ii, or, if a less technical description is desired, Miss Sollas's contribution to the 'Cambridge Natural History,' vol. i, in which special attention is paid to Spongilla.

The diagram reproduced in fig. 1 gives a schematic view of a vertical section through a living freshwater sponge. Although it represents the structure of the organism as being very much simpler than is actually the case, and entirely omits the skeleton, it will be found useful as indicating the main features of the anatomy.

Fig. 1.—Diagram of a vertical section through a freshwater sponge
(modified from Kükenthal)

A=pores; B=subdermal cavity; C=inhalent canal; D=ciliated chamber; E=exhalent canal; F=osculum; G=dermal membrane; H=eggs; J=gemmule.

It will be noted that the diagram represents an individual with a single osculum or exhalent aperture. As a rule adult Demospongiæ have several or many oscula, but even in the Spongillidæ sponges occur in which there is only one. New oscula are formed by a kind of proliferation that renders the structure still more complex than it is when only one exhalent aperture is present.

The little arrows in the figure indicate the direction of the currents of water that pass through the sponge. It enters through small holes in the derma into a subdermal cavity, which separates the membrane from the bulk of the sponge. This space differs greatly in extent in different species. From the subdermal space the water is forced by the action of the flagella into narrow tubular canals that carry it into the ciliated chambers. Thence it passes into other canals, which communicate with what remains of the central cavity, and so out of the oscula.

The ciliated chambers are very minute, and the collar-cells excessively so. It is very difficult to examine them owing to their small size and delicate structure. Fig. 2 D represents a collar-cell of a sponge seen under a very high power of the microscope in ideal conditions.

Fig. 2.—Sponge cells.

A=bubble-cells of Ephydatia mülleri, × 350 (after Weltner). B=gemmule-cell of Spongilla lacustris containing green corpuscles (shaded dark), × 800 (after Weltner). C=gemmule-cell of Ephydatia blembingia showing "tabloids" of food-material, × 1150 (after Evans). D=collar-cell of Esperella ægagrophila, × 1600 (after Vosmaer and Pekelharing). E=three stages in the development of a gemmule-spicule of E. blembingia (after Evans), × 665. F=outline of porocytes of S. proliferens, × ca. 1290: e=dermal cell; n=nucleus; p=pore; p.c.=pore-cell.

The nature of the inhalent apertures in the external membrane has been much discussed as regards the Demospongiæ, but the truth seems to be that their structure differs considerably even in closely allied species. At any rate this is the case as regards the Indian Spongillæ. In all species the membrane is composed of flattened cells of irregular shape fitted together like the pieces of a puzzle-picture. In some species (e. g., Spongilla carteri) the apertures in the membrane consist merely of spaces between adjacent cells, which may be a little more crowded together than is usual. But in others (e. g., Spongilla proliferens and Spongilla crassissima) in which the pores are extremely small, each pore normally pierces the middle of a flat, ring-shaped cell or porocyte. Occasionally, however, a pore may be found that is enclosed by two narrow, crescent-shaped cells joined together at their tips to form a ring. The porocytes of sponges like Spongilla carteri are probably not actually missing, but instead of being in the external membrane are situated below the derma at the external entrance to the canals that carry water to the flagellated chambers or even at the entrance to the chambers themselves[^[L]]. Some authors object on theoretical grounds to the statement that porocytes exist in the Demospongia, and it is possible that these cells have in this grade neither the same origin as, nor a precisely similar function to, the porocytes of other sponges. When they occur in the dermal membrane no great difficulty is experienced in seeing them under a sufficiently high power of the microscope, if the material is well preserved and mounted and stained in a suitable manner[^[M]]. In most sponges the porocytes can contract in such a way that the aperture in their centre is practically closed, but this power appears to be possessed by the porocytes of Spongilla only to a very limited extent, although they closely resemble the porocytes of other sponges in appearance.

The external membrane in many Spongillidæ is prolonged round and above the oscula so as to form an oscular collar. This structure is highly contractile, but cannot close together. As a rule it is much more conspicuous in living sponges than in preserved specimens.

It is not necessary to deal here with most of the cells that occur in the parenchyma or gelatinous part of the sponge. A full list of the kinds that are found is given by Dr. Weltner in his "Spongillidenstudien, V," p. 276 (Arch. Naturg. Berlin, lxxiii (i), 1907). One kind must, however, be briefly noticed as being of some systematic importance, namely the "bubble-cells" (fig. 2 A) that are characteristic of some species of Ephydatia and other genera. These cells are comparatively large, spherical in form; each of them contains a globule of liquid which not only occupies the greater part of the cell, but forces the protoplasm to assume the form of a delicate film lining the cell-wall and covering the globule. In optical section "bubble-cells" have a certain resemblance to porocytes, but the cell is of course imperforate and not flattened.

Skeleton and Spicules.

Radial sections of fragments of the skeletons of Spongillæ

A, S. crassissima var. crassior (from Rajshahi); B, S. carteri (from Calcutta); a=transverse, b=radiating fibres; e=external surface of the sponge.

In the Spongillidæ the spicules and the skeleton are more important as regards the recognition of genera and species than the soft parts. The skeleton is usually reticulate, but sometimes consists of a mass of spicules almost without arrangement. The amount of spongin present is also different in different species. The spicules in a reticulate skeleton are arranged so as to form fibres of two kinds—radiating fibres, which radiate outwards from the centre of the sponge and frequently penetrate the external membrane, and transverse fibres, which run across from one radiating fibre to another. The fibres are composed of relatively large spicules (megascleres) arranged parallel to one another, overlapping at the ends, and bound together by means of a more or less profuse secretion of spongin. In some species they are actually enclosed in a sheath of this substance. The radiating fibres are usually more distinct and stouter than the transverse ones, which are often represented by single spicules but are sometimes splayed out at the ends so as to assume in outline the form of an hour-glass (fig. 3 B). The radiating fibres frequently raise up the membrane at their free extremities just as a tent-pole does a tent.

Normal spicules of the skeleton are always rod-like or needle-like, and either blunt or pointed at both ends; they are either smooth, granular, or covered with small spines. Sometimes spicules of the same type form a more or less irregular transverse network at the base or on the surface of the sponge.

Fig. 4.—Part of an oscular collar of Spongilla lacustris subsp. reticulata, showing arrangement of microscleres in the derma (magnified).

From the systematist's point of view, the structure of the free spicules found scattered in the substance and membrane of the sponge, and especially of those that form the armature of the gemmules, is of more importance than that of the skeleton-spicules. Free spicules are absent in many species; when present they are usually needle-like and pointed at the tips. In a few species, however, they are of variable or irregular form, or consist of several or many shafts meeting in a common central nodule. In one genus (Corvospongilla) they resemble a double grappling-iron in form, having a circle of strongly recurved hooks at both ends. The free microscleres, or flesh-spicules as they are often called, are either smooth, granular, or spiny.

Gemmule-spicules, which form a characteristic feature of the Spongillidæ, are very seldom absent when the gemmules are mature. They are of the greatest importance in distinguishing the genera. In their simplest form they closely resemble the free microscleres, but in several genera they bear, either at or near one end or at or near both ends, transverse disks which are either smooth or indented round the edge. In one genus (Pectispongilla) they are provided at both ends not with disks but with vertically parallel rows of spines resembling combs in appearance.

The simpler spicules of the Spongillidæ are formed in single cells (see fig. 2 E), but those of more complicated shape are produced by several cells acting in concert. Each spicule, although it is formed mainly of hydrated silica (opal), contains a slender organic filament running along its main axis inside the silica. This filament, or rather the tube in which it is contained, is often quite conspicuous, and in some species (e. g., Spongilla crassissima) its termination is marked at both ends of the megasclere by a minute conical protuberance in the silica.

Unless sponges are alchemists and can transmute one element into another, the material of which the spicules are made must ultimately come from the water in which the sponges live, or the rocks or other bodies to or near which they are attached. The amount of water that must pass through a large specimen of such a sponge as Spongilla carteri in order that it may obtain materials for its skeleton must be enormous, for silica is an insoluble substance. I have noticed, however, that this sponge is particularly abundant and grows with special luxuriance in ponds in which clothes are washed with soap, and my friend Mr. G. H. Tipper has suggested to me that possibly the alkali contained in the soap-suds may assist the sponge in dissolving out the silica contained in the mud at the bottom of the ponds. The question of how the mineral matter of the skeleton is obtained is, however, one about which we know nothing definite.

The spongin that binds the skeleton-spicules together takes the form of a colourless or yellowish transparent membrane, which is often practically invisible. When very abundant it sometimes extends across the nodes of the skeleton as a delicate veil. In some sponges it also forms a basal membrane in contact with the object to which the sponge is attached, and in some such cases the spongin of the radiating fibres is in direct continuity with that of the basal membrane.

Colour and Odour.

Most freshwater sponges have a bad odour, which is more marked in some species than in others. This odour is not peculiar to the Spongillidæ, for it is practically identical with that given out by the common marine sponge Halichondria panicea. Its function is probably protective, but how it is produced we do not know.

The coloration of freshwater sponges is usually dull and uniform, but Pectispongilla aurea is of the brilliant yellow indicated by its name, while many species are of the bright green shade characteristic of chlorophyll, the colouring matter of the leaves of plants. Many species are brown or grey, and some are almost white.

These colours are due to one of three causes, or to a combination of more than one of them, viz.:—(1) the inhalation of solid inorganic particles, which are engulfed by the cells; (2) the presence in the cells of coloured substances, solid or liquid, produced by the vital activities of the sponge; and (3) the presence in the cells of peculiar organized living bodies known as "green corpuscles."

Sponges living in muddy water are often nearly black. This is because the cells of their parenchyma are gorged with very minute solid particles of silt. If a sponge of the kind is kept in clean water for a few days, it often becomes almost white. An interesting experiment is easily performed to illustrate the absorption and final elimination of solid colouring matter by placing a living sponge (small specimens of Spongilla carteri are suitable) in a glass of clean water, and sprinkling finely powdered carmine in the water. In a few hours the sponge will be of a bright pink colour, but if only a little carmine is used at first and no more added, it will regain its normal greyish hue in a few days.

The colouring matter produced by the sponge itself is of two kinds—pigment, which is probably a waste product, and the substances produced directly by the ingestion of food or in the process of its digestion. When pigment is produced it takes the form of minute granules lying in the cells of the parenchyma, the dermal membrane being as a rule colourless. Very little is known about the pigments of freshwater sponges, and even less about the direct products of metabolism. It is apparently the latter, however, that give many otherwise colourless sponges a slight pinkish or yellowish tinge directly due to the presence in cells of the parenchyma of minute liquid globules. In one form of Spongilla carteri these globules turn of a dark brown colour if treated with alcohol. The brilliant colour of Pectispongilla aurea is due not to solid granules but to a liquid or semi-liquid substance contained in the cells.

The green corpuscles of the Spongillidæ are not present in all species. There is every reason to think that they represent a stage in the life-history of an alga, and that they enter the sponge in an active condition (see p. 49).

A fourth cause for the coloration of freshwater sponges may be noted briefly. It is not a normal one, but occurs commonly in certain forms (e. g., Spongilla alba var. bengalensis). This cause is the growth in the canals and substance of the sponge of parasitic algaæ, which turn the whole organism of a dull green colour. They do not do so, however, until they have reduced it to a dying state. The commonest parasite of the kind is a filamentous species particularly common in brackish water in the Ganges delta.

External Form and Consistency.

Fig. 5.—Part of a type-specimen of Spongilla lacustris subsp. reticulata (nat. size).

The external form of sponges is very variable, but each species, subspecies, or variety of the Spongillidæ has normally a characteristic appearance. The European race of Spongilla lacustris, for example, consists in favourable circumstances of a flattened basal part from which long cylindrical branches grow out; while in the Indian race of the species these branches are flattened instead of being cylindrical, and anastomose freely. The structure of the branches is identical with that of the basal part. Many other species (for instance, Spongilla bombayensis and S. ultima) never produce branches but always consist of lichenoid or cushion-shaped masses. The appearance of Spongilla crateriformis, when it is growing on a flattened surface which allows it to develop its natural form, is very characteristic, for it consists of little flattened masses that seem to be running out towards one another, just as though the sponge had been dropped, spoonful by spoonful, in a viscous condition from a teaspoon. Some species, such as Trochospongilla phillottiana, cover large areas with a thin film of uniform thickness, while others (e. g., Spongilla alba and Ephydatia meyeni) consist of irregular masses, the surface of which bears numerous irregular ridges or conical, subquadrate, or digitate processes. In a few forms (e. g., Corvospongilla burmanica) the surface is covered with small turret-like projections of considerable regularity, and some (e. g., Spongilla crassissima) naturally assume a spherical or oval shape with an absolutely smooth surface.

The production of long branches is apparently rare in tropical freshwater sponges.

The form of the oscula is characteristic in many cases. No other Indian species has them so large, or with such well-defined margins as Spongilla carteri (Pl. II, fig. 1). In many species (Pl. II, fig. 3) they have a stellate appearance owing to the fact that grooves in the substance of the sponge radiate round them beneath the external membrane. In other species they are quite inconspicuous and very small.

Fig. 6.—Radial section through part of a dried sponge of Spongilla crassissima (from Calcutta), × 5.

Spongillidæ differ greatly in consistency. Spongilla crassissima and Corvospongilla lapidosa are almost stony, although the former is extremely light, more like pumice than true stone. Other species (e. g., Trochospongilla latouchiana) are hard but brittle, while others again are soft and easily compressed, as Spongilla lacustris, the variety mollis of S. carteri, and S. crateriformis. The consistency of a sponge depends on two factors—the number of spicules present, and the amount of spongin. In Corvospongilla lapidosa the number of spicules is very large indeed. They are not arranged so as to form a reticulate skeleton but interlock in all directions, and there is hardly any spongin associated with them. In Spongilla crassissima, on the other hand, the number of spicules although large is not unusually so; but they form a very definitely reticulate skeleton, and are bound together by an unusually profuse secretion of spongin. In S. carteri var. mollis both spicules and spongin are reduced to a minimum, and the parenchyma is relatively more bulky than usual.

Variation.

Sponges are very variable organisms, and even a slight change in the environment of the freshwater species often produces a considerable change in form and structure. Some species vary in accordance with the season, and others without apparent cause. Not only have many given rise to subspecies and "varieties" that possess a certain stability, but most if not all are liable to smaller changes that apparently affect both the individual and the breed, at any rate for a period.

(a) Seasonal Variation.

Weltner has shown in a recent paper (Arch. Natg. Berlin, lxxiii (i), p. 276, 1907) that in Europe those individuals of Ephydatia which are found (exceptionally) in an active condition in winter differ considerably both as regards the number of their cells and their anatomy from those found in summer. In Calcutta the majority of the individuals of Spongilla carteri that are found in summer have their external surface unusually smooth and rounded, and contain in their parenchyma numerous cells the protoplasm of which is gorged with liquid. These cells give the whole sponge a faint pinkish tinge during life; but if it is plunged in spirit, both the liquid in the cells and the spirit turn rapidly of a dark brown colour. Specimens of Spongilla crateriformis taken in a certain tank in Calcutta during the cold weather had the majority of the skeleton-spicules blunt, while the extremities of the gemmule-spicules were distinctly differentiated. Specimens of the same species taken from the same tank in July had the skeleton-spicules pointed, while the extremities of the gemmule-spicules were much less clearly differentiated. I have been unable to confirm this by observations made on sponges from other tanks, but it would certainly suggest that at any rate the breed of sponges in the tank first investigated was liable to seasonal variation.

(b) Variation due directly to Environment.

The characteristic external form of freshwater sponges is liable in most cases to be altered as a direct result of changes in the environment. The following are two characteristic instances of this phenomenon.

Certain shrubs with slender stems grow in the water at the edge of Igatpuri Lake. The stems of these shrubs support many large examples of Spongilla carteri, which are kept in almost constant motion owing to the action of the wind on those parts of the shrubs that are not under water. The surface of the sponges is so affected by the currents of water thus set up against it that it is covered with deep grooves and high irregular ridges like cockscombs. Less than a hundred yards from the lake there is a small pond in which Spongilla carteri is also abundant. Here it grows on stones at the bottom and has the characteristic and almost smooth form of the species.

My second instance also refers in part to Igatpuri Lake. Corvospongilla lapidosa is common in the lake on the lower surface of stones, and also occurs at Nasik, about thirty miles away, on the walls of a conduit of dirty water. In the latter situation it has the form of large sheets of a blackish colour, with the surface corrugated and the oscula inconspicuous, while in the clear waters of the lake it is of a pale yellowish colour, occurs in small lichenoid patches, and has its oscula rendered conspicuous, in spite of their minute size, by being raised on little conical eminences in such a way that they resemble the craters of volcanoes in miniature.

Both the European and the Indian races of Spongilla lacustris fail to develop branches if growing in unfavourable conditions. In specimens obtained from the River Spree near Berlin these structures are sometimes many inches in length; while in mature specimens taken under stones in Loch Baa in the Island of Mull the whole organism consisted of a minute cushion-shaped mass less than an inch in diameter, and was also deficient in spicules. Both these breeds belong to the same species, and probably differ as a direct result of differences in environment.

(c) Variation without apparent cause.

[Plate I] in this volume illustrates an excellent example of variation in external form to which it is impossible to assign a cause with any degree of confidence. The three specimens figured were all taken in the same pond, and at the same season, but in different years. It is possible that the change in form, which was not peculiar to a few individuals but to all those in several adjacent ponds, was due to a difference in the salinity of the water brought about by a more or less abundant rainfall; but of this I have been able to obtain no evidence in succeeding years.

Many Spongillidæ vary without apparent cause as regards the shape, size, and proportions of their spicules. This is the case as regards most species of Euspongilla and Ephydatia, and is a fact to which careful consideration has to be given in separating the species.

Nutrition.

Very little is known about the natural food of freshwater sponges, except that it must be of an organic nature and must be either in a very finely divided or in a liquid condition. The cells of the sponge seem to have the power of selecting suitable food from the water that flows past them, and it is known that they will absorb milk. The fact that they engulf minute particles of silt does not prove that they lack the power of selection, for extraneous matter is taken up by them not only as food but in order that it may be eliminated. Silt would soon block up the canals and so put a stop to the vital activity of the sponge, if it were not got rid of, and presumably it is only taken into the cells in order that they may pass it on and finally disgorge it in such a way or in such a position that it may be carried out of the oscula. The siliceous part of it may be used in forming spicules.

It is generally believed that the green corpuscles play an important part in the nutrition of those sponges in which they occur, and there can be no doubt that these bodies have the power peculiar to all organisms that produce chlorophyll of obtaining nutritive substances direct from water and carbonic oxide through the action of sunlight. Possibly they hand on some of the nourishment thus obtained to the sponges in which they live, or benefit them by the free oxygen given out in the process, but many Spongillidæ do well without them, even when living in identical conditions with species in which they abound.

Reproduction.

Both eggs and buds are produced by freshwater sponges (the latter rarely except by one species), while their gemmules attain an elaboration of structure not observed in any other family of sponges.

Probably all Spongillidæ are potentially monœcious, that is to say, able to produce both eggs and spermatozoa. In one Indian species, however, in which budding is unusually common (viz. Spongilla proliferens), sexual reproduction takes place very seldom, if ever. It is not known whether the eggs of sponges are fertilized by spermatozoa from the individual that produces the egg or by those of other individuals, but not improbably both methods of fertilization occur.

The egg of a freshwater sponge does not differ materially from that of other animals. When mature it is a relatively large spherical cell containing abundant food-material and situated in some natural cavity of the sponge. In the earlier stages of its growth, however, it exhibits amœboid movements, and makes its way through the common jelly. As it approaches maturity it is surrounded by other cells which contain granules of food-material. The food-material is apparently transferred by them in a slightly altered form to the egg. The egg has no shell, but in some species (e. g. Ephydatia blembingia[^[N]]) it is surrounded, after fertilization, by gland-cells belonging to the parent sponge, which secrete round it a membrane of spongin. Development goes on within the chamber thus formed until the larva is ready to assume a free life.

The spermatozoon is also like that of other animals, consisting of a rounded head and a lash-like tail, the movements of which enable it to move rapidly through the water. Spermatozoa are produced in Spongilla from spherical cells not unlike the eggs in general appearance. The contents of these cells divide and subdivide in such a way that they finally consist of a mass of spermatozoa surrounded by a single covering cell, which they finally rupture, and so escape.

Fig. 7.—Diagram of a vertical section through the gemmule of Spongilla proliferens.

A=cellular contents; B=internal chitinous layer; C=external chitinous layer; D=pneumatic coat; E=gemmule-spicule; F=external membrane; G=foraminal tubule.

Gemmules are asexual reproductive bodies peculiar to the sponges, but not to the Spongillidæ. They resemble the statoblasts of the phylactolæmatous polyzoa in general structure as well as in function, which is mainly that of preserving the race from destruction by such agencies as drought, starvation, and temperatures that are either too high or too low for its activities. This function they are enabled to perform by the facts that they are provided with coverings not only very hard but also fitted to resist the unfavourable agencies to which the gemmules are likely to be exposed, and that they contain abundant food-material of which use can be made as soon as favourable conditions occur again.

Internally the gemmule consists of a mass of cells containing food-material in what may be called a tabloid form, for it consists of minutely granular plate-like bodies. These cells are enclosed in a flask-like receptacle, the walls of which consist of two chitinous layers, a delicate inner membrane and an outer one of considerable stoutness. The mouth of the flask is closed by an extension of the inner membrane, and in some species is surrounded by a tubular extension of the external membrane known as the foraminal tubule. Externally the gemmule is usually covered by what is called a "pneumatic coat," also of "chitin" (spongin), but usually of great relative thickness and honeycombed by spaces which contain air, rendering the structure buoyant. The pneumatic coat also contains the microscleres characteristic of the species; it is often limited externally by a third chitinous membrane, on which more gemmule-spicules sometimes lie parallel to the surface.

The cells from which those of the gemmules are derived are akin in origin to those that give rise to eggs and spermatozoa. Some zoologists are therefore of the opinion that the development of the gemmule is an instance of parthenogenesis—that is to say of an organism arising from an egg that has not been fertilized. But some of the collar-cells, although most of them originate from the external ciliated cells of the larva, have a similar origin. The building-up of the gemmule affords an excellent instance of the active co-operation that exists between the cells of sponges, and of their mobility, for the food-material that has to be stored up is brought by cells from all parts of the sponge, and these cells retire after discharging their load into those of the young gemmule.

The formation of the gemmule of Ephydatia blembingia, a Malayan species not yet found in India, is described in detail by Dr. R. Evans (Q. J. Microsc. Sci. London, xliv, p. 81, 1901).

Gemmules are produced by the freshwater sponges of Europe, N. America and Japan at the approach of winter, but in the tropical parts of India they are formed more frequently at the approach of the hot weather (p. 4). After they are fully formed the sponge that has produced them dies, and as a rule disintegrates more or less completely. In some species, however, the greater part of the skeleton remains intact, if it is not disturbed, and retains some of the gemmules in its meshwork, where they finally germinate. Other gemmules are set free. Some of them float on the surface of the water; others sink to the bottom. In any case all of them undergo a period of quiescence before germinating. It has been found that they can be kept dry for two years without dying.

The function of the special spicules with which the gemmules of the Spongillidæ are provided appears to be not only to protect them but more especially to weight them to the extent suitable to the habits of each species. Species that inhabit running water, for example, in some cases have heavier gemmule-spicules than those that live in stagnant water, and their gemmules are the less easily carried away by the currents of the river. The gemmules of sponges growing in lakes are sometimes deficient in spicules. This is the case as regards the form of Spongilla lacustris found in Lake Baa, Isle of Mull, as regards S. helvetica from the Lake of Geneva, S. moorei from Lake Tanganyika, and S. coggini from Tali-Fu in Yunnan; also as regards the species of Spongilla and Ephydatia found in Lake Baikal, many of the sponges of which are said never to produce gemmules.

Except in the genus Corvospongilla and the subgenus Stratospongilla, in both of which the air-spaces of the gemmules are usually no more than cavities between different chitinous membranes, the pneumatic coat is either "granular" or "cellular." Neither of these terms, however, must be understood in a physiological sense, for what appear to be granules in a granular coat are actually minute bubbles of air contained in little cavities in a foam-like mass of chitin (or rather spongin), while the cells in a cellular one are only larger and more regular air-spaces with thin polygonal walls and flat horizontal partitions. The walls of these spaces are said in some cases to contain a considerable amount of silica.

The gemmules with their various coverings are usually spherical in shape, but in some species they are oval or depressed in outline. They lie as a rule free in the substance of the sponge, but in some species adhere at its base to the object to which it is attached. In some species they are joined together in groups, but in most they are quite free one from another.

Reproductive buds[^[O]] are produced, so far as is known, by very few Spongillidæ, although they are common enough in some other groups of sponges. In the only freshwater species in which they have been found to form a habitual means of reproduction, namely in Spongilla proliferens, they have much the appearance of abortive branches, and it is possible that they have been overlooked for this reason in other species, for they were noticed by Laurent in Spongilla lacustris as long ago as 1840 (CR. Sé. Acad. Sci. Paris, xi, p. 478). The buds noticed by Laurent, however, were only produced by very young sponges, and were of a different nature from those of S. proliferens, perhaps representing a form of fission rather than true budding (see 'Voyage de la Bonite: Zoophytologie,' Spongiaires, pl. i (Paris, 1844)).

In Spongilla proliferens, a common Indian species, the buds arise as thickenings of the strands of cells accompanying the radiating spicule-fibres of the skeleton, which project outwards from the surface of the sponge. The thickenings originate beneath the surface and contain, at the earliest stage at which I have as yet examined them, all the elements of the adult organism (i. e. flesh-spicules, ciliated chambers, efferent and afferent canals, parenchyma-cells of various sorts) except skeleton fibres, gemmules, and a dermal membrane. A section at this period closely resembles one of an adult sponge, except that the structure is more compact, the parenchyma being relatively bulky and the canals of small diameter.

Laurent observed reproduction by splitting in young individuals of Spongilla, but I have not been able to obtain evidence myself that this method of reproduction occurs normally in Indian species. In injured specimens of Spongilla carteri, however, I have observed a phenomenon that seems to be rather an abnormal form of budding, little rounded masses of cells making their way to the ends of the radiating skeleton fibres and becoming transformed into young sponges, which break loose and so start an independent existence. Possibly the buds observed by Laurent in S. lacustris were of a similar nature.

Development.

(a) From the Egg.

After fertilization, the egg, lying in its cavity in the sponge, undergoes a complete segmentation; that is to say, becomes divided into a number of cells without any residuum remaining. The segmentation, however, is not equal, for it results in the formation of cells of two distinct types, one larger and less numerous than the other. As the process continues a pear-shaped body is produced, solid at the broader end, which consists of the larger cells, but hollow at the other. Further changes result in the whole of the external surface becoming ciliated or covered with fine protoplasmic lashes, each of which arises from a single small cell; considerable differentiation now takes place among the cells, and spicules begin to appear. At this stage or earlier (for there seem to be differences in different species and individuals as to the stage at which the young sponge escapes) the larva makes its way out of the parent sponge. After a brief period of free life, in which it swims rapidly through the water by means of its cilia, it fixes itself by the broad end to some solid object (from which it can never move again) and undergoes a final metamorphosis. During this process the ciliated cells of the external layer make their way, either by a folding-in of the whole layer or in groups of cells, into the interior, there change into collar-cells and arrange themselves in special cavities—the ciliated chambers of the adult. Finally an osculum, pores, &c., are formed, and the sponge is complete.

This, of course, is the merest outline of what occurs; other changes that take place during the metamorphosis are of great theoretical interest, but cannot be discussed here. The student may refer to Dr. R. Evans's account of the larval development of Spongilla lacustris in the Q. J. Microsc. Sci. London, xlii, p. 363 (1899).

(b) From the Gemmule.

The period for which the gemmule lies dormant probably depends to some extent upon environment and to some extent on the species to which it belongs. Carter found that if he cleaned gemmules with a handkerchief and placed them in water exposed to sunlight, they germinated in a few days; but in Calcutta gemmules of Spongilla alba var. bengalensis treated in this way and placed in my aquarium at the beginning of the hot weather, did not germinate until well on in the "rains." Even then, after about five months, only a few of them did so. Zykoff found that in Europe gemmules kept for two years were still alive and able to germinate.

Germination consists in the cellular contents of the gemmule bursting the membrane or membranes in which they are enclosed, and making their way out of the gemmule in the form of a delicate whitish mass, which sometimes issues through the natural aperture in the outer chitinous coat and sometimes through an actual rent in this coat. In the latter case the development of the young sponge is more advanced than in the former.

The fullest account of development from the gemmule as yet published is by Zykoff, and refers to Ephydatia in Europe (Biol. Centralbl. Berlin, xii, p. 713, 1892).

His investigations show that the bursting of the gemmule is not merely a mechanical effect of moisture or any such agency but is due to development of the cellular contents, which at the time they escape have at least undergone differentiation into two layers. Of the more important soft structures in the sponge the osculum is the first to appear, the ciliated chambers being formed later. This is the opposite of what occurs in the case of the bud, but in both cases the aperture appears to be produced by the pressure of water in the organism. The manner and order in which the different kinds of cells originate in the sponge derived from a gemmule give support to the view that the primitive cell-layers on which morphologists lay great stress are not of any great importance so far as sponges are concerned.

(c) Development of the Bud.

As the bud of Spongilla proliferens grows it makes its way up the skeleton-fibre to which it was originally attached, pushing the dermal membrane, which expands with its growth, before it. The skeleton-fibre does not, however, continue to grow in the bud, in which a number of finer fibres make their appearance, radiating from a point approximately at the centre of the mass. As the bud projects more and more from the surface of the sponge the dermal membrane contracts at its base, so as finally to separate it from its parent. Further details are given on p. 74.

Habitat.

Mr. Edward Potts[^[P]], writing on the freshwater sponges of North America, says:—"These organisms have occasionally been discovered growing in water unfit for domestic uses; but as a rule they prefer pure water, and in my experience the finest specimens have always been found where they are subjected to the most rapid currents." True as this is of the Spongillidæ of temperate climates, it is hardly applicable to those of tropical India, for in this country we find many species growing most luxuriantly and commonly in water that would certainly be considered unfit for domestic purposes in a country in which sanitation was treated as a science. Some species, indeed, are only found in ponds of water polluted by human agency, and such ponds, provided that other conditions are favourable, are perhaps the best collecting grounds. Other favourable conditions consist in a due mixture of light and shade, a lack of disturbance such as that caused by cleaning out the pond, and above all in the presence of objects suitable for the support of sponges.

I do not know exactly why light and shade must be mixed in a habitat favourable for the growth of sponges, for most species prefer shade, if it be not too dense; but it is certainly the case that, with a few exceptions, Indian Spongillidæ flourish best in water shaded at the edges by trees and exposed to sunlight elsewhere. One of the exceptions to this rule is the Indian race of Spongilla lucustris, which is found in small pools of water in sand-dunes without a particle of shade. Several species are only found on the lower surface of stones and roots in circumstances which do not suggest that their position merely protects them from mud, which, as Mr. Potts points out, is their "great enemy." A notable instance is Trochospongilla pennsylvanica, which is found hiding away from light in America and Europe as well as in India.

It is curious that it should be easy to exterminate the sponges in a pond by cleaning it out, for one would have thought that sufficient gemmules would have remained at the edge, or would have been brought rapidly from elsewhere, to restock the water. Mr. Green has, however, noted that Spongilla carteri has disappeared for some years from a small lake at Peradeniya in which it was formerly abundant, owing to the lake having been cleaned out, and I have made similar observations on several occasions in Calcutta.

The question of the objects to which sponges attach themselves is one intimately connected with that of the injury done them by mud. The delta of the Ganges is one of the muddiest districts on earth. There are no stones or rocks in the rivers and ponds, but mud everywhere. If a sponge settles in the mud its canals are rapidly choked, its vital processes cease, and it dies. In this part of India, therefore, most sponges are found fixed either to floating objects such as logs of wood, to vertical objects such as the stems of bulrushes and other aquatic plants, or to the tips of branches that overhang the water and become submerged during the "rains." In Calcutta man has unwittingly come to the assistance of the sponges, not only by digging tanks but also by building "bathing-ghats" of brick at the edge, and constructing, with æsthetic intentions if not results, masses of artificial concrete rocks in or surrounding the water. There are at least two sponges (the typical form of Spongilla alba and Ephydatia meyeni) which in Calcutta are only found attached to such objects. The form of S. alba, however, that is found in ponds of brackish water in the Gangetic delta has not derived this artificial assistance from man, except in the few places where brick bridges have been built, and attaches itself to the stem and roots of a kind of grass that grows at the edge of brackish water. This sponge seems to have become immune even to mud, the particles of which are swallowed by its cells and finally got rid of without blocking up the canals.

Several Indian sponges are only found adhering to stones and rocks. Among these species Corvospongilla lapidosa and our representatives of the subgenus Stratospongilla are noteworthy. Some forms (e. g. Spongilla carteri and S. crateriformis) seem, however, to be just as much at home in muddy as in rocky localities, although they avoid the mud itself.

There is much indirect evidence that the larvæ of freshwater sponges exercise a power of selection as regards the objects to which they affix themselves on settling down for life.

Few Spongillidæ are found in salt or brackish water, but Spongilla alba var. bengalensis has been found in both, and is abundant in the latter; indeed, it has not been found in pure fresh water. Spongilla travancorica has only been found in slightly brackish water, while S. lacustris subsp. reticulata and Dosilia plumosa occur in both fresh and brackish water, although rarely in the latter. The Spongillidæ are essentially a freshwater family, and those forms that are found in any but pure fresh water must be regarded as aberrant or unusually tolerant in their habits, not as primitive marine forms that still linger halfway to the sea.

Animals and Plants commonly associated with Freshwater Sponges.

(a) Enemies.

Freshwater sponges have few living enemies. Indeed, it is difficult to say exactly what is an enemy of a creature so loosely organized as a sponge. There can be little doubt, in any case, that the neuropteroid larva (Sisyra indica) which sucks the cells of several species should be classed in this category, and it is noteworthy that several species of the same genus also occur in Europe and N. America which also attack sponges. Other animals that may be enemies are a midge larva (Tanypus sp.) and certain worms that bore through the parenchyma (p. 93), but I know of no animal that devours sponges bodily, so long as they are uninjured. If their external membrane is destroyed, they are immediately attacked by various little fish and also by snails of the genera Limnæa and Planorbis, and prawns of the genus Palæmon.

Their most active and obvious enemy is a plant, not an animal,—to wit, a filamentous alga that blocks up their canals by its rapid growth (p. 79).

(b) Beneficial Organisms.

The most abundant and possibly the most important organisms that may be considered as benefactors to the Spongillidæ are the green corpuscles that live in the cells of certain species (fig. 2, p. 31), notably Spongilla lacustris, S. proliferens, and Dosilia plumosa. I have already said that these bodies are in all probability algæ which live free in the water and move actively at one stage of their existence, but some of them are handed on directly from a sponge to its descendants in the cells of the gemmule. In their quiescent stage they have been studied by several zoologists, notably by Sir Ray Lankester[^[Q]] and Dr. W. Weltner[^[R]], but the strongest light that has been cast on their origin is given by the researches of Dr. F. W. Gamble and Mr. F. Keeble (Q. J. Microsc. Sci. London, xlvii, p. 363, 1904, and li, p. 167, 1907). These researches do not refer directly to the Spongillidæ but to a little flat-worm that lives in the sea, Convoluta roscoffiensis. The green corpuscles of this worm so closely resemble those of Spongilla that we are justified in supposing a similarity of origin. It has been shown by the authors cited that the green corpuscles of the worm are at one stage minute free-living organisms provided at one end with four flagella and at the other with a red pigment spot. The investigators are of the opinion that these organisms exhibit the essential characters of the algæ known as Chlamydomonadæ, and that after they have entered the worm they play for it the part of an excretory system.

As they exist in the cells of Spongilla the corpuscles are minute oval bodies of a bright green colour and each containing a highly refractile colourless granule. A considerable number may be present in a single cell. It is found in European sponges that they lose their green colour if the sponge is not exposed to bright sunlight. In India, however, where the light is stronger, this is not always the case. Even when the colour goes, the corpuscles can still be distinguished as pale images of their green embodiment. They are called Chlorella by botanists, who have studied their life-history but have not yet discovered the full cycle. See Beyerinck in the Botan. Zeitung for 1890 (vol. xlviii, p. 730, pl. vii; Leipzig), and for further references West's 'British Freshwater Algæ,' p. 230 (1904).

The list of beneficent organisms less commonly present than the green corpuscles includes a Chironomus larva that builds parchment-like tubes in the substance of Spongilla carteri and so assists in supporting the sponge, and of a peculiar little worm (Chætogaster spongillæ[^[S]]) that appears to assist in cleaning up the skeleton of the same sponge at the approach of the hot weather and in setting free the gemmules (p. 93).

(c) Organisms that take shelter in the Sponge or adhere to it externally.

There are many animals which take shelter in the cavities of the sponge without apparently assisting it in any way. Among these are the little fish Gobius alcockii, which lays its eggs inside the oscula of S. carteri, thus ensuring not only protection but also a proper supply of oxygen for them (p. 94); the molluscs (Corbula, spp.) found inside S. alba var. bengalensis (p. 78); and the Isopod (Tachæa spongillicola) that makes its way into the oscula of Spongilla carteri and S. crateriformis (pp. 86, 94).

In Europe a peculiar ciliated Protozoon (Trichodina spongillæ) is found attached to the external surface of freshwater sponges. I have noticed a similar species at Igatpuri on Spongilla crateriformis, but it has not yet been identified. It probably has no effect, good or bad, on the sponge.

Freshwater Sponges in relation to Man.

In dealing with Spongilla carteri I have suggested that sponges may be of some hygienic importance in absorbing putrid organic matter from water used both for ablutionary and for drinking purposes, as is so commonly the case with regard to ponds in India. Their bad odour has caused some species of Spongillidæ to be regarded as capable of polluting water, but a mere bad odour does not necessarily imply that they are insanitary.

Unless my suggestion that sponges purify water used for drinking purposes by absorbing putrid matter should prove to be supported by fact, the Spongillidæ cannot be said to be of any practical benefit to man. The only harm that has been imputed to them is that of polluting water[^[T]], of blocking up water-pipes by their growth—a very rare occurrence,—and of causing irritation to the human skin by means of their spicules—a still rarer one. At least one instance is, however, reported in which men digging in a place where a pond had once been were attacked by a troublesome rash probably due to the presence of sponge-spicules in the earth, and students of the freshwater sponges should be careful not to rub their eyes after handling dried specimens.

Indian Spongillidæ Compared With Those of Other Countries.

In Weltner's catalogue of the freshwater sponges (1895) seventy-six recent species of Spongillidæ (excluding Lubosmirskia) are enumerated, and the number now known is well over a hundred. In India we have twenty-nine species, subspecies, and varieties, while from the whole of Europe only about a dozen are known. In the neighbourhood of Calcutta nine species, representing three genera and a subgenus, have been found; all of them occur in the Museum tank. The only other region of similar extent that can compare with India as regards the richness of its freshwater sponge fauna is that of the Amazon, from which about twenty species are known. From the whole of North America, which has probably been better explored than any other continent so far as Spongillidæ are concerned, only twenty-seven or twenty-eight species have been recorded.

The Indian species fall into seven genera, one of which (Spongilla) consists of three subgenera. With one exception (that of Pectispongilla, which has only been found in Southern India) these genera have a wide distribution over the earth's surface, and this is also the case as regards the subgenera of Spongilla. Four genera (Heteromeyenia, Acalle, Parmula, and Uruguaya) that have not yet been found in India are known to exist elsewhere.

Five of the Indian species are known to occur in Europe, viz., Spongilla lacustris, S. crateriformis, S. carteri, S. fragilis, Trochospongilla pennsylvanica; while Ephydatia meyeni is intermediate between the two commonest representatives of its genus in the Holarctic Zone, Ephydatia fluviatilis and E. mülleri. Of the species that occur both in India and in Europe, two (Spongilla lacustris and S. fragilis) are found in this country in forms sufficiently distinct to be regarded as subspecies or local races. Perhaps this course should also be taken as regards the Indian forms of S. carteri, of which, however, the commonest of the Indian races would be the typical one; but S. crateriformis and T. pennsylvanica seem to preserve their specific characters free from modification, whether they are found in Europe, Asia, or America.

The freshwater sponges of Africa have been comparatively little studied, but two Indian species have been discovered, S. bombayensis in Natal and S. alba var. cerebellata in Egypt. Several of the species from the Malabar Zone are, moreover, closely allied to African forms (p. 11).

Fossil Spongillidæ.

The Spongillidæ are an ancient family. Young described a species (Spongilla purbeckensis) from the Upper Jurassic of Dorset (Geol. Mag. London (new series) v, p. 220 (1878)), while spicules, assigned by Ehrenberg to various genera but actually those of Spongilla lacustris or allied forms, have been found in the Miocene of Bohemia (see Ehrenberg's 'Atlas für Micro-Geologie,' pl. xi (Leipzig, 1854), and Traxler in Földt. Közl., Budapest, 1895, p. 211). Ephydatia is also known in a fossil condition, but is probably less ancient than Spongilla.

Ehrenberg found many sponge spicules in earth from various parts of the Indian Empire (including Baluchistan, Mangalore, Calcutta, the Nicobars and Nepal) and elsewhere, and it might be possible to guess at the identity of some of the more conspicuous species figured in his 'Atlas.' The identification of sponges from isolated spicules is, however, always a matter of doubt, and in some cases Ehrenberg probably assigned spicules belonging to entirely different families or even orders to the same genus, while he frequently attributed the different spicules of the same species to different genera. Among his fossil (or supposed fossil) genera that may be assigned to the Spongillidæ wholly or in part are Aphidiscus, Spongolithis, Lithastericus and Lithosphæridium, many of the species of these "genera" certainly belonging to Spongilla and Ephydatia.

Oriental Spongillidæ not yet found in India.

Few freshwater sponges that have not been found in India are as yet known from the Oriental Region, and there is positive as well as negative evidence that Spongillidæ are less abundant in Malaysia than in this country. The following list includes the names of those that have been found, with notes regarding each species. It is quite possible that any one of them may be found at any time within the geographical boundaries laid down for this 'Fauna.' I have examined types or co-types in all cases except that of Ephydatia fortis, Weltner.

I. Spongilla (Euspongilla) microsclerifera*, Annandale (Philippines). P. U.S. Mus. xxxvii, p. 131 (1909).

This sponge is closely related to S. lacustris, but apparently does not produce branches. It is remarkable for the enormous number of microscleres in its parenchyma.

II. S. (Euspongilla) philippinensis*, Annandale (Philippines). P. U.S. Mus. xxxvi, p. 629 (1909).

Related to S. alba and still more closely to S. sceptrioides of Australia. From the former it is readily distinguished by having minutely spined megascleres, green corpuscles, slender gemmule-spicules with short spines and no free microscleres.

III. S. (? Euspongilla) yunnanensis*, Annandale (W. China). Rec. Ind. Mus. v, p. 197 (1910).

Apparently allied to S. philippinensis but with smooth skeleton-spicules and a more delicate skeleton.

IV. S. (Stratospongilla) sinensis*, Annandale (Foochow, China). P. U.S. Mus. xxxviii, p. 183 (1910).

This species and S. clementis are referred to Stratospongilla with some doubt. Their gemmules are intermediate in structure between those of that subgenus and those of Euspongilla. In S. sinensis the gemmules are packed together in groups at the base of the sponge, and their spicules are smooth, stout, and gradually pointed.

V. S. (Stratospongilla) clementis*, Annandale (Philippines). P. U.S. Mus. xxxvi, p. 631 (1909).

The gemmules are single and closely adherent at the base of the sponge. Their spicules are very slender and minutely spined.

VI. S. (? Stratospongilla) coggini*, Annandale (W. China). Rec. Ind. Mus. v, p. 198 (1910).

The gemmules apparently lack microscleres. They resemble those of S. clementis, to which the species is probably related, in other respects. The skeleton-spicules are spiny and rather stout, the species being strongly developed at the two ends.

VII. S. (Stratospongilla) sumatrana*, Weber (Malay Archipelago). Zool. Ergebnisse einer Reise in Niederländisch Ost-Indien, i. p. 38 (1890).

Closely allied to S. indica (p. 100) but with pointed skeleton-spicules.

VIII. Ephydatia fortis, Weltner (Philippines). Arch. Naturgesch. lxi(i), p. 141 (1895).

This species is remarkable for the great development of the spines on the shaft of the gemmule-spicules.

IX. Ephydatia bogorensis*, Weber (Malay Archipelago). Zool. Ergebnisse einer Reise in Niederländisch Ost-Indien, i, p. 33 (1890).

The gemmule-spicules have rather narrow flattish disks, the edge of which is feebly but closely serrated.

X. E. blembingia*, Evans (Malay Peninsula). Q. J. Microsc. Sci. London, xliv, p. 81 (1901).

The gemmules resemble those of Dosilia plumosa but are spherical. There are no free microscleres.

XI. Tubella vesparium*, v. Martens (Borneo). Arch. Naturg. Berlin, xxxiv, p. 62 (1868).

Closely related to T. vesparioides (p. 189), but with spiny megascleres.

As regards Spongilla decipiens*, Weber, from the Malay Archipelago, see p. 97.

II.

History of the Study of Freshwater Sponges.

The bath-sponge was known to the Greeks at an early date, and Homer refers to it as being used for cleansing furniture, for expunging writing, and for ablutionary purposes. He also mentions its peculiar structure, "with many holes." "Many things besides," wrote the English naturalist Ray in his 'Historia Plantarum' (1686), "regarding the powers and uses of sponges have the Ancients: to them refer." Ray himself describes at least one freshwater species, which had been found in an English river, and refers to what may be another as having been brought from America. In the eighteenth century Linné, Pallas and other authors described the commoner European Spongillidæ in general terms, sometimes as plants and sometimes as animals, more usually as zoophytes or "plant-animals" partaking of the nature of both kingdoms. The gemmules were noted and referred to as seeds. The early naturalists of the Linnæan Epoch, however, added little to the general knowledge of the Spongillidæ, being occupied with theory in which theological disputes were involved rather than actual observation, and, notwithstanding the fact that the animal nature of sponges was clearly demonstrated by Ellis[^[U]] in 1765, it was not until the nineteenth century was well advanced that zoologists could regard sponges in anything like an impartial manner.

One of the pioneers in the scientific study of the freshwater forms was the late Dr. H. J. Carter, who commenced his investigations, and carried out a great part of them, in Bombay with little of the apparatus now considered necessary, and with a microscope that must have been grossly defective according to modern ideas. His long series of papers (1848-1887) published in the 'Annals and Magazine of Natural History' is an enduring monument to Indian zoology, and forms the best possible introduction to the study of the Spongillidæ. Even his earlier mistakes are instructive, for they are due not so much to actual errors in observation as to a faithful transcription of what was observed with faulty apparatus.

Contemporary with Carter were two authors whose monographs on the freshwater sponges did much to advance the study of the group, namely, J. S. Bowerbank, whose account of the species known at the time was published in the 'Proceedings of the Zoological Society of London' in 1882, and the veteran American naturalist Mr. Edward Potts, whose study of the freshwater sponges culminated in his monograph published in the 'Proceedings of the Academy of Natural Sciences of Philadelphia' in 1887. Carter's own revision of the group was published in the 'Annals and Magazine of Natural History' in 1881. The names of Vejdovsky, who prefaced Potts's monograph with an account of the European species, and of Dybowsky, who published several important papers on classification, should also be mentioned, while Weltner's catalogue of the known species (1895) is of the greatest possible value to students of the group.

Many authors have dealt with the physiology, reproduction and development of the Spongillidæ, especially in recent years; Dr. R. Evans's description of the larva of Spongilla lacustris (1899), and his account of the development of the gemmule in Ephydatia blembingia (1901), Zykoff's account of the development of the gemmule and of the sponge from the gemmule (1892), and Weltner's observations on colour and other points (1893, 1907), may be mentioned in particular. Laurent's observations on development (1844), which were published in the 'Voyage de la Bonite,' and especially the exquisite plates which accompany them, have not received the notice they deserve, probably on account of their method of publication.

Literature.

The fullest account of the literature on the Spongillidæ as yet published will be found in the first of Weltner's 'Spongillidenstudien' (Archiv für Naturgeschichte, lix (i), p. 209, 1893). Unfortunately it contains no references of later date than 1892. The following list is not a complete bibliography, but merely a list of books and papers that should prove of use to students of the Oriental Spongillidæ.

[K] Except in "Proterospongia," an organism of doubtful affinities but not a sponge. It consists of a mass of jelly containing ordinary cells, with collar-cells outside.

[L] Cf. Weltner, "Spongillidenstudien, V," Arch. Naturg. Berlin, lxxiii (i), p. 273 (1907).

[M] It is difficult to see any trace of them in thin microtome sections. A fragment of the membrane must be mounted whole.

[N] Rec. Ind. Mus. i, p. 269 (1907).

[O] Proliferation whereby more than one osculum is produced is really a form of budding, but in most sponges this has become no longer a mode of reproduction but the normal method by which size is increased, and must therefore be considered merely as a vegetative process.

[P] P. Ac. Philad. 1887, p. 162.

[Q] Q. J. Microsc. Sci. London, xxii. p. 229 (1882).

[R] Arch. Naturg. Berlin, lix (i), p. 260 (1893).

[S] Journ. As. Soc. Beng. n. s. ii, 1906, p. 189.

[T] See Potts, Proc. Ac. Philad. 1884, p. 28.

[U] Phil. Trans. Roy. Soc. lv, p. 280.

[V] Descriptions of Siberian sponges are not included in these references.

GLOSSARY OF TECHNICAL TERMS USED IN PART I.

SYSTEMATIC LIST OF THE INDIAN SPONGILLIDÆ.

[Types, schizotypes, or cotypes have been examined in the case of all species, &c. , whose names are marked thus, *.]

Genus 1. Spongilla, Lamarck (1816).

Subgenus A. Euspongilla, Vejdovsky (1883).

1.

? S. lacustris, auct. (perhaps in N.W. India).

1a.

S. lacustris subsp. reticulata*, Annandale (1907).

2.

S. proliferens*, Annandale (1907).

3.

S. alba*, Carter (1849).

3a.

S. alba var. cerebellata, Bowerbank (1863).

3b.

S. alba var. bengalensis*, Annandale (1906).

4.

S. cinerea*, Carter (1849).

5.

S. travancorica*, Annandale (1909).

6.

S. hemephydatia*, Annandale (1909).

7.

S. crateriformis* (Potts) (1882).

Subgenus B. Eunapius, J. E. Gray (1867).

8.

S. carteri*, Carter (1849).

8a.

S. carteri var. mollis*, nov.

8b.

S. carteri var. cava*, nov.

8c.

S. carteri var. lobosa*, nov.

9a.

S. fragilis subsp. calcuttana*, nov.

9b.

S. fragilis var. decipiens, Weber

(probably Malaysian, not Indian).

10.

S. gemina*, sp. nov.

11.

S. crassissima*, Annandale (1907).

11a.

S. crassissima var. crassior*, Annandale (1907).

Subgenus C. Stratospongilla, Annandale (1909).

12.

S. indica*, Annandale (1908).

13.

S. bombayensis*, Carter (1882).

14.

S. ultima*, Annandale (1910).

Genus 2. Pectispongilla, Annandale (1909).

15.

P. aurea*, Annandale (1909).

15a.

P. aurea var. subspinosa*, nov.

Genus 3. Ephydatia, Lamouroux (1816).

16.

E. meyeni* (Carter) (1849).

Genus 4. Dosilia, J. E. Gray (1867).

17.

D. plumosa* (Carter) (1849).

Genus 5. Trochospongilla, Vejdovsky (1883).

18.

T. latouchiana*, Annandale (1907).

19.

T. phillottiana*, Annandale (1907).

20.

T. pennsylvanica* (Potts) (1882).

Genus 6. Tubella, Carter (1881).

21.

T. vesparioides*, Annandale (1908).

Genus 7. Corvospongilla, nov.

22.

C. burmanica* (Kirkpatrick) (1908).

23.

C. lapidosa* (Annandale) (1908).

Order HALICHONDRINA.

Siliceous monaxon sponges in which the horny skeleton is much reduced or absent and the spicular skeleton is more or less definitely reticulate. The microscleres are usually rod-like and rarely have more than one main axis.

Family SPONGILLIDÆ.

Spongilladæ, J. E. Gray, P. Zool. Soc. London, 1867, p. 550.

Freshwater Halichondrina which at certain seasons produce gemmules armed with peculiar microscleres. Two distinct kinds of microsclere are often present, that associated with the gemmule sometimes consisting of a vertical shaft at the ends of which transverse disks or rotulæ are borne. There is always at least a trace of a subdermal cavity.

Many authors divide the Spongillidæ into two subfamilies:—Spongillinæ (or Euspongillinæ), in which the gemmule-spicules have no transverse rotulæ, and Meyeninæ (or Ephydatiinæ), in which they have rotules at one or both ends. So gradual, however, is the transition that I find it difficult to decide in one instance to which of two genera, typical respectively of the two "subfamilies," a species should be assigned. Minchin in his account of the Porifera in Lankester's "Treatise on Zoology" (1900) regards the Spongillidæ merely as a subfamily of the Heterorrhaphidæ, and there certainly are few differences of a definite nature between them and the marine family (or subfamily) Remeridæ.

Key to the Indian Genera of Spongillidæ.

The most distinct genus of Spongillidæ not yet found in India is Heteromeyenia, Potts. It is easily distinguished from all others by the fact that the birotulate spicules of the gemmule are of two quite distinct kinds, which occur together on every mature gemmule. Heteromeyenia is represented by several American species, one of which has been found in Europe. Acalle, J. E. Gray, which is represented by a single South American species (Spongilla recurvata, Bowerbank), is related to Heteromeyenia but has one kind of gemmule-spicule tubelliform, the other birotulate. Probably Uraguaya, Carter, should be regarded as a subgenus of Trochospongilla with an unusually solid skeleton; it is peculiar to S. America. Parmula, Carter (=Drulia, Gray) includes South American forms allied to Tubella, but with the shaft of the gemmule-spicule degenerate and consisting of a mere projection in the centre of a shield-like body, which represents the lower rotule. The status of Potamolepis, Marshall, originally described from the Lake of Galilee, is very doubtful; possibly some or all of its species belong to the subgenus of Spongilla here called Stratospongilla (p. 100); but they are stated never to produce gemmules. The same is the case as regards Pachydictyum, Weltner, which consists of a single species from Celebes.

The sponges from Lake Baikal assigned by Weltner (Arch. Naturg. lxi (i) p. 131) to the subfamily Lubomirskinæ are of doubtful position and need not be considered here; while Lessepsia, Keller, from one of the salt lakes on the Suez Canal, certainly does not belong to the family, although it is assigned to it by von Lendenfeld (Mon. Horny Sponges, p. 904 (1889)) and subsequently by Minchin (Porifera, p. 152, in Lankester's Treatise on Zoology, part ii (1900)).

Genus 1. SPONGILLA, Lamarck (Carter emend.).

Spongilla, Lamarck, Histoire des Animaux sans Vertèbres, ii, p. 111 (1836). Spongilla, Carter, Ann. Nat. Hist. (5) vii, p. 86 (1881). Euspongilla, Vejdovsky, Abh. Böhm. Ges. xii, p. 15 (1883). Spongilla, Potts, P. Ac. Philad. 1887, p. 182.

Type, Spongilla lacustris, auctorum.

Spongillidæ in which the gemmules have (normally) cylindrical or subcylindrical spicules that are sharp or blunt at the ends, without a distinct transverse disk or disks and without comb-like vertical rows of spines.

The skeleton is variable in structure, sometimes being almost amorphous, sometimes having well-defined radiating and transverse fibres firmly compacted with spongin. The skeleton-spicules are either sharp or blunt at the ends. Flesh-spicules are often absent; when present they are needle-like and resemble the gemmule-spicules in general structure; they have not even rudimentary rotules at their ends. The gemmules either lie free in the substance of the sponge or are attached to its support; sometimes they adhere together in free or attached groups.

Spongilla is undoubtedly the most primitive genus of the Spongillidæ, its spicules showing less sign of specialization than those of any other genus included in the family. As a fossil it goes back at any rate to the Upper Jurassic (p. 52).

Geographical Distribution.—Cosmopolitan. In most countries the majority of the freshwater sponges belong to this genus, but in Japan Ephydatia seems to predominate.

Key to the Indian Species of Spongilla.

Subgenus A. EUSPONGILLA, Vejdovsky.

Euspongilla, Vejdovsky, Abh. Böhm. Ges. xii, p. 15 (1883). Euspongilla, id., in Potts's "Fresh-Water Sponges," P. Ac. Philad. 1887, p. 172. Euspongilla, Weltner, in Zacharias's Tier- und Pflanzenwelt des Süsswassers, i, p. 210 (1891).

Type, Spongilla lacustris, auctorum.

Spongillæ in which the gemmules are covered with a thick, apparently granular pneumatic coat. A delicate membrane often occurs outside this coat, but it is never thick or horny. The gemmules usually lie free in the sponge but sometimes adhere to its support; rarely they are fastened together in groups (e. g. in S. aspinosa, Potts). The skeleton-spicules are never very stout and the skeleton is always delicate.

The species in this subgenus are closely allied and must be distinguished rather by the sum of their peculiarities than by any one character. They occur in all countries in which Spongillidæ are found. Seven Indian species may be recognized.

1. Spongilla lacustris, auctorum.

Spongilla lacustris, Bowerbank, P. Zool. Soc. London, 1863, p. 441, pl. xxxviii, fig. 14. Spongilla lacustris, Carter, Ann. Nat. Hist. (5) vii, p. 87 (1881). Euspongilla lacustris, Vejdovsky, in Potts's "Fresh-Water Sponges," P. Ac. Philad. 1887, p. 172. Spongilla lacustris, Potts, ibid., p. 186, pl. v, fig. 1, pl. vii, figs. 1-6. Euspongilla lacustris, Weltner, in Zacharias's Tier- und Pflanzenwelt des Süsswassers, i, p. 211, figs. 36-38 (1891). Spongilla lacustris, id., Arch. Naturg. lxi (i), pp. 118, 133-135 (1895). Spongilla lacustris, Annandale, J. Linn. Soc., Zool., xxx, p. 245 (1908).

[I have not attempted to give a detailed synonymy of this common species. There is no means of telling whether many of the earlier names given to forms or allies of S. lacustris are actual synonyms, and it would serve no useful purpose, so far as the fauna of India is concerned, to complicate matters by referring to obscure descriptions or possible descriptions of a species only represented in India, so far as we know, by a specialized local race, to which separate references are given.]

Sponge soft and easily compressed, very brittle when dry, usually consisting of a flat or rounded basal portion of no great depth and of long free cylindrical branches, which droop when removed from the water; branches occasionally absent. Colour bright green when the sponge is growing in a strong light, dirty flesh-colour when it is growing in the shade. (Even in the latter case traces of the "green corpuscles" can be detected in the cells of the parenchyma.) Oscula star-shaped, of moderate size, as a rule rendered conspicuous by the furrows that radiate from them over the outer surface of the parenchyma below the external membrane; oscular collars well developed.

Skeleton reticulate, loose, with definite radiating and transverse fibres held together by a small quantity of spongin; the fibres slender but not extremely so.

Spicules. Skeleton-spicules smooth, sharply pointed, long, slender. Flesh-spicules slender, covered with small spines, sharply pointed, nearly straight. Gemmule-spicules resembling the flesh-spicules but shorter and as a rule more strongly curved, sometimes bent so as to form semicircular figures, usually pointed somewhat abruptly; their spines relatively longer than those of the flesh-spicules, often curved backwards, especially near the ends of the spicules, at which points they are often longer than elsewhere.

Gemmules usually numerous in autumn, lying free in the sponge, spherical, variable in size but usually rather large, as a rule covered with a thick granular coat in which the spicules are arranged tangentially; a horizontal layer of spicules often present in the external membrane; the granular coat and its spicules occasionally deficient. No foraminal tubule; its place sometimes taken by an open, bowl-shaped chitinous structure the base of which is in continuity with the inner chitinous coat of the gemmule.

S. lacustris is an extremely variable species, varying in the size, proportions and shape of its spicules, in its external form and in the size and structure of the gemmule. A considerable number of varieties have been described from different parts of Europe and N. America, but some of these may represent distinct but closely-allied species; descriptions of most of them will be found in Potts's "Fresh-Water Sponges." The embryology and the earlier stages of the development from the egg have been described in great detail by Evans (Quart. J. Micr. Sci. (n. s.) xlii, p. 363 (1899)), while the anatomy and physiology are discussed by most authors who have written on these features in the Spongillidæ.

Type.—It is impossible to say who was the first authority to use the name Spongilla lacustris in the sense in which it is used by recent authors. No type can therefore be recognized.

Geographical Distribution.—S. lacustris occurs all over Europe and N. America and is probably the commonest species in most parts of both continents. It has also been found in Northern Asia and may occur in the Himalayan lakes and in the north-west of India.

1 a. Subspecies reticulata*, Annandale.

Spongilla reticulata, Annandale, Rec. Ind. Mus. i, p. 387, pl. xiv, fig. 1 (1907). Spongilla lacustris subspecies reticulata, id., P. U.S. Mus. xxxvii, p. 401 (1909).

This race differs from the typical S. lacustris in the following particulars:—

(1) The branches are always compressed and anastomose freely when well developed (fig. 5, p. [37]);

(2) the skeleton-fibres are finer;

(3) the skeleton-spicules are longer;

(4) the gemmule-spicules are longer and more slender and are never strongly bent.

As regards the form of the skeleton- and gemmule-spicules and also that of the branches the subspecies reticulata resembles S. alba rather than S. lacustris, but owing to the fact that it agrees with S. lacustris in its profuse production of branches, in possessing green corpuscles and in its fragility, I think it should be associated with that species.

Fig. 8.

A=gemmule-spicules of Spongilla lacustris subsp. reticulata (from type); B=gemmule-spicules of S. alba from Calcutta: both highly magnified.

The branches are sometimes broad (fig. 5, p. 37), sometimes very slender. In the latter condition they resemble blades of grass growing in the water.

Type in the Indian Museum; a co-type in the British Museum.

Geographical Distribution.—All over Eastern India and Burma; also in the Bombay Presidency. Localities:—Bengal, Port Canning, Ganges delta; Rajshahi (Rampur Bhulia) on the Ganges, 150 miles N. of Calcutta (Annandale); Puri district, Orissa (Annandale); R. Jharai, Siripur, Saran district, Tirhut (M. Mackenzie): Madras Presidency, Madras (town) (J. R. Henderson): Bombay Presidency, Igatpuri, W. Ghats (Annandale).

Biology.—This subspecies is usually found in small masses of water, especially in pools of rain-water, but Mr. Mackenzie found it growing luxuriantly in the Jharai at a time of flood in September. It is very abundant in small pools among the sand-dunes that skirt the greater part of the east coast of India. Here it grows with great rapidity during the "rains," and often becomes desiccated even more rapidly as soon as the rain ceases. As early in the autumn as October I have seen masses of the sponge attached, perfectly dry, to grass growing in the sand near the Sur Lake in Orissa. They were, of course, dead but preserved a life-like appearance. Some of them measured about six inches in diameter. At Port Canning the sponge grows during the rains on the brickwork of bridges over ditches of brackish water that dry up at the beginning of winter, while at Rajshahi and at Igatpuri I found it at the edges of small ponds, at the latter place in November, at the former in February. Specimens taken at Madras by Dr. Henderson during the rains in small ponds in the sand contained no gemmules, but these structures are very numerous in sponges examined in autumn or winter.

Numerous larvæ of Sisyra indica (p. 92) were found in this sponge at Rajshahi. Unlike those obtained from S. alba, they had a green colour owing to the green matter sucked from the sponge in their stomachs. The coralloides phase of Plumatella fruticosa (p. 219) was also found in S. lacustris subsp. reticulata at Rajshahi.

So far as my experience goes, this subspecies has always a bright green colour due to the presence of "green corpuscles," even when it is growing in a pond heavily shaded by trees or under the arch of a small bridge. Probably the more intense light of India enables the corpuscles to flourish in situations in which in Europe they would lose their chlorophyll.

2. Spongilla proliferens*, Annandale.

Spongilla cinerea, Weber (nec Carter), Zool. Ergeb. Niederl. Ost-Ind. vol. i, pp. 35, 46 (1890). Spongilla proliferens, Annandale, J. Asiat. Soc. Bengal, 1907, p. 15, fig. 1. Spongilla proliferens, id., Rec. Ind. Mus. i, pp. 267, 271 (1907).

Sponge forming soft, shallow cushions rarely more than 10 cm. in diameter on the leaves of water-plants, or small irregular masses on their roots and stems. Colour bright green. Oscula moderate, flat, surrounded by deep, cone-shaped collars; radiating furrows and canals in the parenchyma surrounding them often deep. External pores contained normally in single cells. The surface frequently covered by small rounded buds; true branches if present more or less flattened or conical, always short, as a rule absent.

Skeleton loose, feebly reticulate at the base of the sponge; transverse fibres slender in the upper part of the sponge, often scarcely recognizable at its base. Very little spongin present.

Spicules. Skeleton-spicules long, smooth, sharply pointed; the length on an average at least 20 times the greatest breadth, often more. Flesh-spicules slender, gradually pointed, nearly straight, covered with minute straight or nearly straight spines. Gemmule-spicules very similar, but usually a little stouter and often blunt at the ends; their spines rather longer than those on the flesh-spicules, usually more numerous near the ends than in the middle of the spicule, slightly retroverted, those at the extreme tips often so arranged as to suggest a rudimentary rotule.

Fig. 9.—Gemmule of Spongilla proliferens as seen in optical section (from Calcutta), × 140.

Gemmules usually numerous, lying free near the base of the sponge, very variable in size, spherical, surrounded by a thick granular layer in which the spicules, which are always very numerous, are arranged tangentially, their position being more near the vertical than the horizontal; a few horizontal spicules usually present on the external surface of the gemmule, which frequently has a ragged appearance owing to some of the tangential spicules protruding further than others. Foraminal tubule stout, cylindrical, usually somewhat contorted; its orifice irregular in outline. Sometimes more than one foramen present.

S. proliferens can be distinguished from all forms of S. lacustris and S. alba by the fact that its gemmules possess a foraminal tubule; from S. cinerea it can be distinguished by its colour and its smooth skeleton-spicules, and from S. travancorica by its free gemmules. I have been enabled by the kindness of Prof. Max Weber to examine specimens from Celebes and Java identified by him as S. cinerea, Carter, and have no doubt that they belong to my species.

Type in the Indian Museum; a co-type in the British Museum.

Geographical Distribution.—All over Eastern India and Burma; also in Cochin on the west coast; Ceylon; W. China; Java, Flores and Celebes. Localities:—Bengal, Calcutta and neighbourhood (Annandale); Berhampore, Murshidabad district (R. E. Lloyd): Assam, Mangal-dai near the Bhutan frontier (S. W. Kemp): Madras Presidency, Madras (town) and neighbourhood (J. R. Henderson); Rambha, Ganjam district (Annandale); Bangalore, Mysore (alt. ca. 3000 ft.) (Annandale); Ernakulam and Trichur, Cochin (G. Mathai): Burma, Rangoon (Annandale, J. Coggin Brown); Prome, Upper Burma (J. Coggin Brown); Kawkareik, Amherst district, Tenasserim (Annandale): Ceylon, between Maradankawela and Galapita-Gala, North Central Province (Willey). Mr. J. Coggin Brown has recently brought back specimens from Yunnan.

Biology.—S. proliferens is usually found in ponds which never dry up; Prof. Max Weber found it in small streams in Malaysia. It is common in India on the leaves of Vallisneria and Limnanthemum, on the roots of Pistia stratiotes and on the stems of rushes and grass. So far as I have been able to discover, the life of the individual sponge is short, only lasting a few weeks.

Sexual reproduction occurs seldom or never, but reproduction by means of buds and gemmules continues throughout the year. The former is a rare method of reproduction in most Spongillidæ but in this species occurs normally and constantly, the buds being often very numerous on the external surface. They arise a short distance below the surface as thickenings in the strands of cells that accompany the radiating fibres of the skeleton. As they grow they push their way up the fibres, forcing the external membrane outwards. The membrane contracts gradually round their bases, cuts off communication between them and the parent sponge and finally sets them adrift. No hole remains when this takes place, for the membrane closes up both round the base of the bud and over the aperture whence it has emerged.

The newly liberated bud already possesses numerous minute pores, but as yet no osculum; its shape exhibits considerable variation, but the end that was farthest from the parent-sponge before liberation is always more or less rounded, while the other end is flat. The size also varies considerably. Some of the buds float, others sink. Those that float do so either owing to their shape, which depends on the degree of development they have reached before liberation, or to the fact that a bubble of gas is produced in their interior. The latter phenomenon only occurs when the sun is shining on the sponge at the moment they are set free, and is due to the action of the chlorophyll of the green bodies so abundant in certain of the parenchyma cells of this species. If the liberation of the bud is delayed rather longer than usual, numbers of flesh-spicules are produced towards the ends of the primary skeleton-fibres and spread out in one plane so as to have a fan-like outline; in such buds the form is more flattened and the distal end less rounded than in others, and the superficial area is relatively great, so that they float more readily. Those buds that sink usually fall in such a way that their proximal, flattened end comes in contact with the bottom or some suspended object, to which it adheres. Sometimes, however, owing to irregularity of outline in the distal end, the proximal end is uppermost. In this case it is the distal end that adheres. Whichever end is uppermost, it is in the uppermost end, or as it may now be called, the upper surface, that the osculum is formed. Water is drawn into the young sponge through the pores and, finding no outlet, accumulates under the external membrane, the subdermal cavity being at this stage even larger than it is in the adult sponge. Immediately after adhesion the young sponge flattens itself out. This process apparently presses together the water in the subdermal cavity and causes a large part of it to accumulate at one point, which is usually situated near the centre of the upper surface. A transparent conical projection formed of the external membrane arises at this point, and at the tip of the cone a white spot appears. What is the exact cause of this spot I have not yet been able to ascertain, but it marks the point at which the imprisoned water breaks through the expanded membrane, thus forming the first osculum. Before the aperture is formed, it is already possible to distinguish on the surface of the parenchyma numerous channels radiating from the point at which the osculum will be formed to the periphery of the young sponge. These channels as a rule persist in the adult organism and result from the fact that the inhalent apertures are situated at the periphery, being absent from both the proximal and the distal ends of the bud. In the case of floating buds the course of development is the same, except that the osculum, as in the case of development from the gemmule in other species (see Zykoff, Biol. Centrbl. xii, p. 713, 1892), is usually formed before adhesion takes place.

The sponge of S. proliferens is usually too small to afford shelter to other animals, and I have not found in it any of those commonly associated with S. carteri and S. alba.

Owing to its small size S. proliferens is more easily kept alive in an aquarium than most species, and its production of buds can be studied in captivity. In captivity a curious phenomenon is manifested, viz. the production of extra oscula, often in large numbers. This is due either to a feebleness in the currents of the sponge which makes it difficult to get rid of waste substances or to the fact that the canals get blocked. The effluent water collects in patches under the external membrane instead of making its way out of the existing oscula, and new oscula are formed over these patches in much the same way as the first osculum is formed in the bud.

3. Spongilla alba*, Carter.

Spongilla alba, Carter, J. Bombay Asiat. Soc. iii, p. 32, pl. i, fig. 4 & Ann. Nat. Hist. (2) iv, p. 83, pl. iii, fig. 4 (1849) Spongilla alba, Bowerbank, P. Zool. Soc. London, 1863, p. 463 pl. xxxviii, fig. 15. Spongilla alba, Carter, Ann. Nat. Hist. (5) vii, p. 88 (1881). Spongilla alba, Petr, Rozp. Ceske Ak. Praze, Trída, ii, pl. i, figs. 3-6 (1899) (text in Czech). Spongilla alba, Annandale, Rec. Ind. Mus. i, p. 388, pl. xiv, fig. 2 (1907).

Sponge forming masses of considerable area, but never of more than moderate depth or thickness. Surface smooth and undulating or with irregular or conical projections; sponge hard but brittle; colour white or whitish; oscula of moderate or large size, never very conspicuous; radiating furrows absent or very short; external membrane adhering to the substance of the sponge.

Skeleton forming a moderately dense network of slender radiating and transverse fibres feebly held together; little spongin present; the meshes much smaller than in S. lacustris or S. proliferens.

Spicules. Skeleton-spicules smooth, sharply pointed, slender, feebly curved. Gemmule-spicules (fig. 8, p. 71) slender, cylindrical, blunt or abruptly pointed at the ends, feebly curved, bearing relatively long backwardly directed spines, which are usually more numerous at the ends than near the middle of the shaft. Flesh-spicules very numerous in the parenchyma and especially the external membrane, as a rule considerably more slender and more sharply pointed than the gemmule-spicules, covered with straight spines which are often longer at the middle of the shaft than at the ends.

Gemmules usually of large size, with a moderately thick granular layer; spicules never very numerous, often lying horizontally on the external surface of the gemmule as well as tangentially in the granular layer; no foraminal tubule; a foraminal cup sometimes present.

3a. Var. cerebellata, Bowerbank.

Spongilla cerebellata, Bowerbank, P. Zool. Soc. London, 1863, p. 465, pl. xxxviii, fig. 16. Spongilla alba var. cerebellata, Carter, Ann. Nat. Hist. (5) vii, p. 88 (1881). Spongilla cerebellata, Weltner, Arch. Naturg. lxi (i), p. 117 (1895). Spongilla cerebellata, Kirkpatrick, Ann. Nat. Hist. (7) xx, p. 523 (1907).

This variety is distinguished from the typical form by the total absence of flesh-spicules. The gemmule-spicules are also more numerous and cross one another more regularly.

3b. Var. bengalensis*, Annandale. ([Plate I], figs. 1-3.)

Spongilla lacustris var. bengalensis, Annandale, J. Asiat. Soc. Bengal, 1906, p. 56. Spongilla alba var. marina, id., Rec. Ind. Mus. i, p. 389 (1907).

The sponge is either devoid of branches or produces irregular, compressed, and often digitate processes, sometimes of considerable length and delicacy. Flesh-spicules are usually present throughout the sponge, but are sometimes absent from one part of a specimen and present in others. Some of the gemmules are often much smaller than the others. Perhaps this form should be regarded as a phase rather than a true variety (see p. 18).

All forms of S. alba can be distinguished from all forms of S. lacustris by the much closer network of the skeleton and by the consequent hardness of the sponge; also by the complete absence of green corpuscles.

Types. The types of the species and of the var. cerebellata are in the British Museum, with fragments of the former in the Indian Museum; that of var. bengalensis is in the Indian Museum, with a co-type in London.

Geographical Distribution.—India and Egypt. Localities:—Bombay Presidency, island of Bombay (Carter); Igatpuri, W. Ghats (Annandale): Bengal, Calcutta; Port Canning, Ganges delta (var. bengalensis) (Annandale); Garia, Salt Lakes, nr. Calcutta (var. bengalensis) (B. L. Chaudhuri); Chilka Lake, Orissa (var. bengalensis) (Gopal Chunder Chatterjee): Madras Presidency, Rambha, Ganjam district (Annandale): Nizam's Territory, Aurangabad (Bowerbank, var. cerebellata). The var. cerebellata has also been taken near Cairo.

Biology.—The typical form of the species is usually found growing on rocks or bricks at the edges of ponds, while the variety bengalensis abounds on grass-roots in pools and swamps of brackish water in the Ganges delta and has been found on mussel-shells (Modiola jenkinsi, Preston) in practically salt water in the Chilka Lake. Carter procured the typical form at Bombay on stones which were only covered for six months in the year, and "temporarily on floating objects." In Calcutta this form flourishes in the cold weather on artificial stonework in the "tanks" together with S. carteri, S. fragilis, Ephydatia meyeni, and Trochospongilla latouchiana.

The variety bengalensis is best known to me as it occurs in certain ponds of brackish water at Port Canning on the Mutlah River, which connects the Salt Lakes near Calcutta with the sea. It appears in these ponds in great luxuriance every year at the beginning of the cold weather and often coats the whole edge for a space of several hundred feet, growing in irregular masses which are more or less fused together on the roots and stems of a species of grass that flourishes in such situations. Apparently the tendency for the sponges to form branches is much more marked in some years than in others (see Pl. I, figs. 1-3). The gemmules germinate towards the end of the "rains," and large masses of sponge are not formed much before December. At this season, however, the level of the water in the ponds sinks considerably and many of the sponges become dry. If high winds occur, the dry sponges are broken up and often carried for considerable distances over the flat surrounding country. In January the gemmules floating on the surface of the ponds form a regular scum. S. alba var. bengalensis is the only sponge that occurs in these ponds at Port Canning, but S. lacustris, subsp. reticulata, is occasionally found with it on brickwork in the ditches that drain off the water from the neighbouring fields into the Mutlah estuary. The latter sponge, however, perishes as these ditches dry up, at an earlier period than that at which S. alba reaches its maximum development.

The larvæ of Sisyra indica are commonly found in the oscula of the typical form of S. alba as well as in those of S. lacustris subsp. reticulata, and S. carteri; but the compact structure of the sponge renders it a less suitable residence for other incolæ than S. carteri.

In the variety bengalensis, as it grows in the ponds at Port Canning, a large number of arthropods, molluscs and other small animals take shelter. Apart from protozoa and rotifers, which have as yet been little studied, the following are some of the more abundant inhabitants of the sponge:—The sea-anemone, Sagartia schilleriana subsp. exul (see p. 140), which frequently occurs in very large numbers in the broader canals; the free-living nematode, Oncholaimus indicus[^[W]], which makes its way in and out of the oscula; molluscs belonging to several species of the genus Corbula, which conceal themselves in the canals but are sometimes engulfed in the growing sponge and so perish; young individuals of the crab Varuna litterata, which hide among the branches and ramifications of the larger sponges together with several small species of prawns and the schizopod Macropsis orientalis[^[X]]; the peculiar amphipod Quadrivisio bengalensis[^[Y]], only known from the ponds at Port Canning, which breeds in little communities inside the sponge; a small isopod[^[Z]], allied to Sphæroma walkeri, Stebbing; the larva of a may-fly, and those of at least two midges (Chironomidæ).

The peculiarly mixed nature (marine and lacustrine) of the fauna associated with S. alba in the ponds at Port Canning is well illustrated by this list, and it only remains to be stated that little fish (Gobius alcockii, Barbus stigma, Haplochilus melanostigma, H. panchax, etc.) are very common and feed readily on injured sponges. They are apparently unable to attack a sponge so long as its external membrane is intact, but if this membrane is broken, they swarm round the sponge and devour the parenchyma greedily. In fresh water one of these fishes (Gobius alcockii, see p. 94) lays its eggs in sponges.

The chief enemy of the sponges at Port Canning is, however, not an animal but a plant, viz., a green filamentous alga which grows inside the sponge, penetrating its substance, blocking up its canals and so causing it to die. Similar algæ have been described as being beneficial to the sponges in which they grow[^[AA]], but my experience is that they are deadly enemies, for the growth of such algæ is one of the difficulties which must be fought in keeping sponges alive in an aquarium. The alga that grows in S. alba often gives it a dark green colour, which is, however, quite different from the bright green caused by the presence of green corpuscles. The colour of healthy specimens of the variety bengalensis is a rather dark grey, which appears to be due to minute inorganic particles taken into the cells of the parenchyma from the exceedingly muddy water in which this sponge usually grows. If the sponge is found in clean water, to whichever variety of the species it belongs, it is nearly white with a slight yellowish tinge. Even when the typical form is growing in close proximity to S. proliferens, as is often the case, no trace of green corpuscles is found in its cells.

4. Spongilla cinerea*, Carter.

Spongilla cinerea, Carter, J. Bombay Soc. iii, p. 30, pl. i, fig. 5, & Ann. Nat. Hist. (2) iv, p. 82, pl. iii, fig. 5 (1849). Spongilla cinerea, Bowerbank, P. Zool. Soc. London, 1863, p. 468, pl. xxxviii, fig. 19. Spongilla cinerea, Carter, Ann. Nat. Hist. (5) vii, p. 263 (1881).

Sponge forming large, flat sheets, never more than a few millimetres in thickness, without a trace of branches, compact but very friable, of a dark greyish colour; oscula small and inconspicuous or moderately large, never prominent; membrane adhering closely to the sponge.

Skeleton with well-defined but slender radiating fibres, which contain very little spongin; transverse fibres close together but consisting for the most part of one or two spicules only.

Spicules. Skeleton-spicules short, slender, sharply pointed, minutely serrated or irregular in outline, almost straight. Gemmule-spicules very small, rather stout, cylindrical, pointed, covered with relatively long and stout spines which are either straight or directed towards the ends of the spicule. Flesh-spicules fairly numerous in the external membrane but by no means abundant in the parenchyma, very slender, gradually pointed, covered uniformly with minute but distinct spines.

Gemmules very small, only visible to the naked eye as minute specks, as a rule numerous, free in the substance of the sponge, each provided with a slender foraminal tubule and covered with a thick granular coat in which the gemmule-spicules are arranged almost horizontally; a horizontal layer of spicules also present on the external surface of the gemmule; gemmule-spicules very numerous.

Fig. 10.—Gemmules and fragment of the skeleton of Spongilla cinerea (from type specimen), × 35.

This sponge is easily distinguished from its Indian allies by the form of its skeleton-spicules, which are, as Bowerbank expresses it, "subspined"; that it to say, under a high power of the microscope their outline appears to be very minutely serrated, although under a low power they seem to be quite smooth. The spicules also are smaller than those of S. alba, the only species with which S. cinerea is likely to be confused, and the gemmule has a well-developed foraminal tubule; the skeleton is much closer than in S. proliferens.

Type in the British Museum; a piece in the Indian Museum.

Geographical Distribution.—S. cinerea is only known from the Bombay Presidency. Carter obtained the original specimens at Bombay and the only ones I have found were collected at Nasik, which is situated on the eastern slopes of the Western Ghats, about 90 miles to the north-east.

Biology.—Carter's specimens were growing on gravel, rocks and stones at the edge of "tanks," and were seldom covered for more than six months in the year. Mine were on the sides of a stone conduit built to facilitate bathing by conveying a part of the water of the Godaveri River under a bridge. They were accompanied by Spongilla indica and Corvospongilla lapidosa (the only other sponges I have found in running water in India) and in the month of November appeared to be in active growth.

5. Spongilla travancorica*, Annandale.

Spongilla travancorica, Annandale, Rec. Ind. Mus. iii, p. 101, pl. xii, fig. 1 (1909).

Sponge small, encrusting, without branches, hard but brittle; its structure somewhat loose; colour dirty white. Dermal membrane in close contact with the skeleton; pores and oscula inconspicuous. Surface minutely hispid, smooth and rounded as a whole.

Skeleton consisting of moderately stout and coherent radiating fibres and well-defined transverse ones; a number of horizontal megascleres present at the base and surface, but not arranged in any definite order. No basal membrane.

Fig. 11.—Microscleres of Spongilla travancorica. A=Gemmule-spicules; B=flesh-spicules (from type specimen), × 240.

Spicules. Skeleton-spicules smooth, pointed at either end, moderately stout, straight or curved, sometimes angularly bent; curvature usually slight. Free microscleres abundant in the dermal membrane, slender, nearly straight, gradually and sharply pointed, profusely ornamented with short straight spines, which are much more numerous and longer at the middle than near the ends. Gemmule-spicules stouter and rather longer, cylindrical, terminating at each end in a sharp spine, ornamented with shorter spines, which are more numerous and longer at the ends than at the middle; at the ends they are sometimes directed backwards, without, however, being curved.

Gemmules firmly adherent to the support of the sponge, at the base of which they form a layer one gemmule thick; each provided with at least one foraminal tubule, which is straight and conical: two tubules, one at the top and one at one side, usually present. Granular layer well developed. Spicules arranged irregularly in this layer, as a rule being more nearly vertical than horizontal but pointing in all directions, not confined externally by a membrane; no external layer of horizontal spicules.

Measurements of Spicules and Gemmules.

This species is easily distinguished from its allies of the subgenus Euspongilla by its adherent gemmules with their (usually) multiple apertures and rough external surface.

Type in the collection of the Indian Museum.

Habitat. Backwater near Shasthancottah, Travancore, in slightly brackish water; on the roots of shrubs growing at the edge; November, 1908 (Annandale).

The specimens were dead when found.

6. Spongilla hemephydatia*, Annandale.

Spongilla hemephydatia, Annandale, Rec. Ind. Mus. iii, p. 275 (1909).

Fig. 12.—Gemmule and spicules of Spongilla hemephydatia (from type specimen).

Sponge soft, fragile, amorphous, of a dirty yellow colour, with large oscula, which are not conspicuously raised above the surface but open into very wide horizontal channels in the substance of the sponge. The oscular collars are fairly well developed, but the subepidermal space is not extensive.

Skeleton diffuse, consisting of very fine radiating fibres, which are crossed at wide and irregular intervals by still finer transverse ones; very little chitinoid substance present.

Spicules. Skeleton-spicules smooth, slender, sharply pointed at both ends, nearly straight. No true flesh-spicules. Gemmule-spicules straight or nearly so, cylindrical, or constricted in the middle, obscurely pointed or blunt, clothed with short, sharp, straight spines, which are very numerous but not markedly longer at the two ends; these spicules frequently found free in the parenchyma.

Gemmules numerous, small, free, spherical, yellow, with a well-developed granular coat (in which the spicules are arranged almost horizontally) and external to it a fine membrane which in preserved specimens becomes puckered owing to unequal contraction; each gemmule with a single aperture provided with a straight, rather wide, but very delicate foraminal tubule.

Measurements of Spicules and Gemmules.

This sponge in its general structure bears a very close resemblance to Spongilla crateriformis.

Type in the collection of the Indian Museum.

Habitat. Growing on weeds at the edge of the Sur Lake, Orissa, October 1908. Only one specimen was taken, together with many examples of S. lacustris subsp. reticulata, S. carteri and S. crassissima.

7. Spongilla crateriformis* (Potts).

Meyenia crateriforma, Potts, P. Ac. Philad. 1882, p. 12. Meyenia crateriformis, id., ibid. 1887, p. 228, pl. v, fig. 6, pl. x, fig. 5. ? Ephydatia crateriformis, Hanitsch, Nature, ii, p. 511 (1895). Ephydatia crateriformis, Weltner, Arch. Naturg. lxi (i), pp. 122, 134 (1895). ? Ephydatia crateriformis, Hanitsch, Irish Natural. iv, p. 125, pl. iv, fig. 5 (1895). Ephydatia indica, Annandale, J. Asiat. Soc. Bengal, 1907, p. 20 (figures poor). Ephydatia indica, id., Rec. Ind. Mus. i, pp. 272, 279, 388, 391 (1907). Ephydatia crateriformis, Scharff, European Animals, p. 34 (1907). Ephydatia crateriformis, Annandale, P. U.S. Mus. xxxvii, p. 402, fig. 1 (1909).

Sponge very fragile, forming soft irregular masses on the roots and stems of water-plants, between which it is sometimes stretched as a delicate film, or thin layers or cushions on flat surfaces. Oscula large, flat, circular, or of irregular shape, opening into broad horizontal canals, which at their distal end are superficial and often covered by the external membrane only. Colour white, yellowish, greyish, or blackish.

Skeleton very delicate; radiating fibres rarely consisting of more than two parallel spicules; transverse fibres far apart, frequently consisting of single spicules; very little spongin present.

Fig. 13.—Spicules of Spongilla crateriformis.

A. From specimen taken in July in a tank on the Calcutta maidan. B. From type specimen of Ephydatia indica taken in the Indian Museum tank in winter. Both figures × 240.

Spicules. Skeleton-spicules feebly curved, slender, as a rule irregular in outline, sometimes almost smooth; the ends as a rule sharply pointed, often constricted off and expanded so as to resemble spear-heads, occasionally blunt. No true flesh-spicules. Gemmule-spicules often free in the parenchyma, cylindrical, slender, very variable in length in different sponges, straight or nearly so, as a rule with an irregular circle of strong straight or recurved spines at either end resembling a rudimentary rotule, and with shorter straight spines scattered on the shaft, sometimes without the rudimentary rotule, either truncate at the ends or terminating in a sharp spine.

Gemmules small, free, each surrounded by a thick granular layer in which the spicules stand upright or nearly so, and covered externally by a delicate but very distinct chitinous membrane; no horizontal spicules; foramen situated at the base of a crater-like depression in the granular coat, which is sometimes raised round it so as to form a conspicuous rampart; a short, straight foraminal tubule.

The shape of the spicules is extremely variable, and sponges in which they are very different occur in the same localities and even in the same ponds. It is possible that the differences are directly due to slight changes in the environment, for in one pond in Calcutta a form with Spongilla-like gemmule-spicules appears to replace the typical form, which is common in winter, during the hot weather and "rains." I have not, however, found this to be the case in other ponds. Perhaps S. hemephydatia will ultimately prove to be a variety of this very variable species, but its smooth and regular skeleton-spicules and short-spined gemmule-spicules afford a ready method of distinguishing it from S. crateriformis. The two sponges are easily distinguished from all others in the subgenus Euspongilla by the upright and regular arrangement of their gemmule-spicules, for although in S. proliferens and S. travancorica some of the gemmule-spicules are nearly vertical, their arrangement is always irregular, a large proportion of the spicules make an acute angle with the inner coat of the gemmule and a few as a rule lie parallel to it. The systematic position of S. crateriformis is almost exactly intermediate between Euspongilla and Ephydatia, to which genus it has hitherto been assigned. I think, however, that taking into consideration its close relationship to S. hemephydatia, it is best to assign it to Spongilla, as its rudimentary rotules never form distinct disks. I have examined some of Potts's original specimens from different American localities and can detect no constant difference between them and Indian specimens.

Types in the United States National Museum; co-types in Calcutta.

Geographical Distribution.—This sponge was originally described from North America (in which continent it is widely distributed) and has been recorded from the west of Ireland with some doubt. In India and Burma it is widely distributed. Bengal, Calcutta and neighbourhood (Annandale); Sonarpur, Gangetic delta (Annandale); Bombay Presidency, Igatpuri Lake, W. Ghats (altitude ca. 2,000 feet) (Annandale); Madras Presidency, neighbourhood of Madras town (J. R. Henderson); Museum compound, Egmore (Madras town) (Annandale); near Bangalore (alt. ca. 3,000 ft.), Mysore State (Annandale); Ernakulam, Cochin (G. Mathai): Burma, Kawkareik, interior of Amherst district, Tenasserim, and the Moulmein waterworks in the same district (Annandale).[^[AB]]

Biology.—S. crateriformis flourishes in Calcutta throughout the year. Here it is usually found adhering to the roots of water-plants, especially Pistia and Limnanthemum. In the case of the former it occurs at the surface, in that of the latter at the bottom. When growing near the surface or even if attached to a stone at the bottom in clear water, it is invariably of a pale yellowish or greyish colour. When growing on the roots of Limnanthemum in the mud of the Gangetic alluvium, however, it is almost black, and when growing in the reddish muddy waters of the tanks round Bangalore of a reddish-brown colour. This appears to be due entirely to the absorption of minute particles of inorganic matter by the cells of the parenchyma. If black sponges of the species are kept alive in clean water, they turn pure white in less than a week, apparently because these particles are eliminated. When growing on stones the sponge, as found in India, often conforms exactly with Potts's description: "a filmy grey sponge, branching off here and there ... yet with a curious lack of continuity...."

The wide efferent canals of this sponge afford a convenient shelter to small crustacea, and the isopod Tachæa spongillicola, Stebbing (see p. 94), is found in them more abundantly than in those of any other sponge. This is especially the case when the sponge is growing at the bottom. On the surface of the sponge I have found a peculiar protozoon which resembles the European Trichodina spongillæ in general structure but belongs, I think, to a distinct species, if not to a distinct genus.

Subgenus B. EUNAPIUS, J. E. Gray.

Eunapius, J. E. Gray (partim), P. Zool. Soc. London, 1867, p. 552. Spongilla (s. str.), Vejdovsky, in Potts's "Fresh-Water Sponges," P. Ac. Philad. 1887, p. 172. Spongilla (s. str.), Weltner, in Zacharias's Tier- und Pflanzenwelt des Süsswassers, i, p. 214 (1891). Spongilla (s. str.), Annandale, Zool. Jahrb., Syst. xxvii, p. 559 (1909).

Type, Spongilla carteri, Carter.

Spongillæ in which the gemmules are covered with layers of distinct polygonal air-spaces with chitinous walls.

The gemmules are usually fastened together in groups, which may either be free in the sponge or adhere to its support as a "pavement layer"; sometimes, however, they are not arranged in this manner, but are quite independent of one another. The skeleton is usually delicate, sometimes very stout (e. g., in S. nitens, Carter).

The term Eunapius here used is not quite in the original sense, for Gray included under it Bowerbank's Spongilla paupercula which is now regarded as a form of S. lacustris. His description, nevertheless, fits the group of species here associated except in one particular, viz., the smoothness of the gemmule-spicules to which he refers, for this character, though a feature of S. carteri, is not found in certain closely allied forms. The use of "Spongilla" in a double sense may be avoided by the adoption of Gray's name.

The subgenus Eunapius is, like Euspongilla, cosmopolitan. It is not, however, nearly so prolific in species. Four can be recognized in India, two of which range, in slightly different forms, as far north as Europe, one of them also being found in North America, Northern Asia, and Australia.

8. Spongilla carteri* Carter (Bowerbank, in litt.). ([Plate II]. fig. 1.)

Spongilla friabilis?, Carter (nec Lamarck), J. Bombay Asiat. Soc. iii, p. 31, pl. i, fig. 3 (1849), & Ann. Nat. Hist. (2) iv, p. 83, pl. ii. fig. 3 (1849). Spongilla carteri, Carter, Ann. Nat. Hist. (3) iii, p. 334, pl. viii, figs. 1-7 (1859). Spongilla carteri, Bowerbank, P. Zool. Soc. London, 1863, p. 469, pl. xxxviii, fig. 20. Eunapius carteri, J. E. Gray, ibid. 1867, p. 552. Spongilla carteri, Carter, Ann. Nat. Hist. (5) vii, p. 86 (1881). Spongilla carteri, id., ibid. x, p. 369 (1882). Spongilla carteri, Potts, P. Ac. Philad. 1887, p. 194. Spongilla carteri, Weltner, Arch. Naturg. lxi (i), pp. 117, 134 (1895). Spongilla carteri, Kirkpatrick, P. Zool. Soc. London, 1906 (i), p. 219, pl. xv, figs. 3, 4 (? figs. 1, 2). Spongilla carteri, Annandale, J. Asiat. Soc. Bengal, 1906, p. 188, pl. i, fig. 1. Spongilla carteri, Willey, Spolia Zeyl. iv, p. 184 (1907). Spongilla carteri, Annandale, ibid. vii, p. 63, pl. 1, fig. 1 (1910).

Fig. 14.—Gemmule of Spongilla carteri (from Calcutta), as seen in optical section, × 140.

Sponge massive, as a rule with the surface smooth and rounded, occasionally bearing irregular ridges, which may even take the form of cockscombs; the oscula large, rounded, conspicuous but not raised above the surface of the sponge, leading into broad vertical canals; the lateral canals, except in the immediate vicinity of the central vertical ones, not very broad; the oscular collars extending for a considerable distance over the oscula in living or well-preserved specimens, never standing out from the surface; the oscula never surrounded by radiating furrows. The inhalent pores surrounded externally by unmodified cells of the external membrane. Colour greyish, sometimes with a flush of green on the external surface.

The sponge has a peculiarly strong and offensive smell.

Skeleton fairly compact, with well-developed radiating fibres; the transverse fibres splayed out at either end so that they sometimes resemble a pair of fans joined together by the handles (fig. 3, p. 33). A moderate amount of spongin present.

Spicules. Skeleton-spicules smooth, pointed, nearly straight, never very stout but somewhat variable in exact proportions. Gemmule-spicules similar but much smaller. (There are no true flesh-spicules, but immature skeleton-spicules may easily be mistaken for them.)

Gemmules as a rule numerous, spherical or flattened at the base, variable in size, each covered by a thick coat consisting of several layers of relatively large polygonal air-spaces. A single aperture surrounded by a crater-like depression in the cellular coat and provided with a foraminal tubule resembling an inverted bottle in shape. (This tubule, which does not extend beyond the surface of the cellular coat, is liable to be broken off in dried specimens.) The spicules variable in quantity, arranged irregularly among the spaces of the cellular coat and usually forming a sparse horizontal layer on its external surface. Each gemmule contained in a cage of skeleton-spicules, by the pressure of which it is frequently distorted.

8a. Var. mollis*, nov.

This variety is characterized by a paucity of skeleton-spicules. The sponge is therefore soft and so fragile that it usually breaks in pieces if lifted from the water by means of its support. Owing to the paucity of skeleton-spicules, which resemble those of the typical form individually, the radiating and transverse fibres are extremely delicate.

Common in Calcutta.

8b. Var. cava*, nov.

This variety is characterized by the fact that the oscula open into broad horizontal canals, the roof of which is formed by a thin layer of parenchyma and skeleton or, in places, of the external membrane only. The skeleton is loose and fragile, and the living sponge has a peculiar glassy appearance. In spirit the colour is yellowish, during life it is greenish or white.

Taken at Bombay; November, 1907.

8c. Var. lobosa*, nov.

The greater part of the sponge in this variety consists of a number of compressed but pointed vertical lobes, which arise from a relatively shallow, rounded base, in which the oscula occur. The dried sponge has a yellowish colour.

Apparently common in Travancore.

* * * * *

I cannot distinguish these three "varieties"[^[AC]] from the typical form as distinct species; indeed, their status as varieties is a little doubtful in two cases out of the three. Var. cava appears to be a variety in the strict sense of the word (see p. 18), for it was found on the island of Bombay, the original locality of the species, growing side by side with the typical form. Var. lobosa, however, should perhaps be regarded as a subspecies rather than a variety, for I have received specimens from two localities in the extreme south-west of India and have no evidence that the typical form occurs in that part of the country. Evidence, however, is rather scanty as regards the occurrence of freshwater sponges in S. India. Var. mollis, again, may be a phase directly due to environment. It is the common form in the ponds of certain parts (e. g. in the neighbourhood of the Maidan and at Alipore) of the Calcutta municipal area, but in ponds in other parts (e. g. about Belgatchia) of the same area, only the typical form is found. It is possible that the water in the former ponds may be deficient in silica or may possess some other peculiarity that renders the production of spicules difficult for S. carteri; but this seems hardly probable, for S. crassissima, a species with a rather dense siliceous skeleton, flourishes in the same ponds. I have noticed that in ponds in which the aquatic vegetation is luxuriant and such genera of plants as Pistia and Limnanthemum flourish, there is always a tendency for S. carteri to be softer than in ponds in which the vegetation is mostly cryptogamic, and in Calcutta those parts of the town in which sponges of this species produce most spicules are those in which a slight infiltration of brackish water into the ponds may be suspected; but in the interior of India, in places where the water is absolutely fresh, hard specimens seem to be the rule rather than the exception.

S. carteri is closely related to S. nitens, Carter (Africa, and possibly S. America), but differs from that species in its comparatively slender, sharp skeleton-spicules and smooth gemmule-spicules. It may readily be distinguished from all other Indian freshwater sponges by its large, deep, round oscula, but this feature is not so marked in var. lobosa as in the other forms. The typical form and var. mollis grow to a larger size than is recorded for any other species of the family. I possess a specimen of the typical form from the neighbourhood of Calcutta which measures 30 × 27 cm. in diameter and 19.5 cm. in depth, and weighs (dry) 24-3/4 oz. The base of this specimen, which is solid throughout, is nearly circular, and the general form is mound-shaped. Another large specimen from Calcutta is in the form of an irregular wreath, the greatest diameter of which is 34 cm. This specimen weighs (dry) 16-1/4 oz. Both these specimens probably represent the growth of several years.

Types.—The types of the varieties mollis, cava and lobosa are in the collection of the Indian Museum. I regard as the type of the species the specimen sent by Carter to Bowerbank and by him named S. carteri, although, owing to some confusion, Carter's description under this name appeared some years before Bowerbank's. This specimen is in the British Museum, with a fragment in the Indian Museum.

Geographical Distribution.—The range of the species extends westwards to Hungary, southwards to Mauritius and eastwards to the island of Madura in the Malay Archipelago; a specimen from Lake Victoria Nyanza in Central Africa has been referred to it by Kirkpatrick (P. Zool. Soc. London, 1906 (i), p. 219), but I doubt whether the identification is correct. In India S. carteri is by far the most universally distributed and usually much the commonest freshwater sponge; it is one of the only two species as yet found in Ceylon. Specimens are known from the following localities:—Punjab, Lahore (J. Stephenson): Bombay Presidency, island of Bombay (Carter, Kirkpatrick, Annandale); Igatpuri, W. Ghats (alt. ca. 2,000 ft.) (Annandale): United Provinces (plains), Agra (Kirkpatrick); Lucknow: Himalayas, Bhim Tal, Kumaon (alt. 4,500 ft.) (Annandale); Tribeni, Nepal (Hodgart): Bengal, Calcutta and neighbourhood; Rajshahi (Rampur Bhulia) on the R. Ganges about 150 miles N. of Calcutta (Annandale); Berhampur, Murshidabad district (R. E. Lloyd); Pusa, Darbbhanga district (Bainbrigge Fletcher); Siripur, Saran district, Tirhut (M. Mackenzie); Puri and the Sur Lake, Orissa (Annandale): Madras Presidency, near Madras town (J. R. Henderson); Madura district (R. Bruce Foote); Bangalore (Annandale) and Worgaum, Mysore State (2,500-3,000 ft.); Ernakulam and Trichur, Cochin (G. Mathai); Trivandrum and the neighbourhood of C. Comorin, Travancore (var. lobosa) (R. S. N. Pillay): Burma, Kawkareik, interior of Amherst district, Tenasserim (Annandale); Rangoon (Annandale); Bhamo, Upper Burma (J. Coggin Brown): Ceylon, Peradeniya (E. E. Green); outlet of the Maha Rambaikulam between Vavuniya and Mamadu, Northern Province (Willey); Horowapotanana, between Trincomalee and Anuradihapura, North-Central Province (Willey).

Biology.—S. carteri usually grows in ponds and lakes; I have never seen it in running water. Mr. Mackenzie found it on the walls of old indigo wells in Tirhut.

The exact form of the sponge depends to some extent on the forces acting on it during life. At Igatpuri, for instance, I found that specimens attached to the stems of shrubs growing in the lake and constantly swayed by the wind had their surface irregularly reticulated with high undulating ridges, while those growing on stones at the bottom of a neighbouring pond were smooth and rounded.

Sponges of this species do not shun the light.

In Calcutta S. carteri flourishes during the cold weather (November to March). By the end of March many specimens that have attached themselves to delicate stems such as those of the leaves of Limnanthemum, or to the roots of Pistia stratiotes, have grown too heavy for their support and have sunk down into the mud at the bottom of the ponds, in which they are quickly smothered. Others fixed to the end of branches overhanging the water or to bricks at the edge have completely dried up. A large proportion, however, still remain under water; but even these begin to show signs of decay at this period. Their cells migrate to the extremities of the sponge, leaving a mass of gemmules in the centre, and finally perish.

Few sponges exist in an active condition throughout the hot weather. The majority of those that do so exhibit a curious phenomenon. Their surface becomes smoothly rounded and they have a slightly pinkish colour; the majority of the cells of their parenchyma, if viewed under a high power of the microscope, can be seen to be gorged with very minute drops of liquid. This liquid is colourless in its natural condition, but if the sponge is plunged into alcohol the liquid turns of a dark brown colour which stains both the alcohol and the sponge almost instantaneously. Probably the liquid represents some kind of reserve food-material. Even in the hot weather a few living sponges of the species may be found that have not this peculiarity, but, in some ponds at any rate, the majority that survive assume the peculiar summer form, which I have also found at Lucknow.

Reproduction takes place in S. carteri in three distinct ways, two of which may be regarded as normal, while the third is apparently the result of accident. If a healthy sponge is torn into small pieces and these pieces are kept in a bowl of water, little masses of cells congregate at the tips of the radiating fibres of the skeleton and assume a globular form. At first these cells are homogeneous, having clear protoplasm full of minute globules of liquid. The masses differ considerably in size but never exceed a few millimetres in diameter. In about two days differentiation commences among the cells; then spicules are secreted, a central cavity and an external membrane formed, and an aperture, the first osculum, appears in the membrane. In about ten days a complete young sponge is produced, but the details of development have not been worked out.

The most common normal form of reproduction is by means of gemmules, which are produced in great numbers towards the end of the cold weather. If small sponges are kept alive in an aquarium even at the beginning of the cold weather, they begin to produce gemmules almost immediately, but these gemmules although otherwise perfect, possess few or no gemmule-spicules. If the sponge becomes desiccated at the end of the cold weather and is protected in a sheltered place, some or all of the gemmules contained in the meshes of its skeleton germinate in situ as soon as the water reaches it again during the "rains." It is by a continuous or rather periodical growth of this kind, reassumed season after season, that large masses of sponge are formed. In such masses it is often possible to distinguish the growth of the several years, but as a rule the layers become more or less intimately fused together, for no limiting membrane separates them. A large proportion of the gemmules are, however, set free and either float on the surface of the water that remains in the ponds or are dried up and carried about by the wind. In these circumstances they do not germinate until the succeeding cold weather, even if circumstances other than temperature are favourable; but as soon as the cold weather commences they begin to produce new sponges with great energy.

Sexual reproduction, the second normal form, takes place in S. carteri mainly if not only at the approach of a change of season, that is to say about March, just before the hot weather commences, and about November, just as the average temperature begins to sink to a temperate level. At these seasons healthy sponges may often be found full of eggs and embryos, which lie in the natural cavities of the sponge without protecting membrane.

In the ponds of Calcutta a large number of animals are found associated in a more or less definite manner with Spongilla carteri. Only one, however, can be described with any degree of certainty as being in normal circumstances an enemy, namely the larva of Sisyra indica,[^[AD]] and even in the case of this little insect it is doubtful how far its attacks are actually injurious to the sponge. The larva is often found in considerable numbers clinging to the oscula and wide efferent canals of S. carteri, its proboscis inserted into the substance of the sponge. If the sponge dies and the water becomes foul the larvæ swim or crawl away. If the sponge dries up, they leave its interior (in which, however, they sometimes remain for some days after it has become dry) and pupate in a silken cocoon on its surface. Hence they emerge as perfect insects after about a week.

An animal that may be an enemy of S. carteri is a flat-worm (an undescribed species of Planaria) common in its larger canals and remarkable for the small size of its pharynx. The same worm, however, is also found at the base of the leaves of bulrushes and in other like situations, and there is no evidence that it actually feeds on the sponge. Injured sponges are eaten by the prawn Palæmon lamarrei, which, however, only attacks them when the dermal membrane is broken. A Tanypus larva (Chironomid Diptera) that makes its way though the substance of the sponge may also be an enemy; it is commoner in decaying than in vigorous sponges.

The presence of another Chironomid larva (Chironomus, sp.) appears to be actually beneficial. In many cases it is clear that this larva and the sponge grow up together, and the larva is commoner in vigorous than in decayed sponges. Unlike the Tanypus larva, it builds parchment-like tubes, in which it lives, on the surface of the sponge. The sponge, however, often grows very rapidly and the larva is soon in danger of being engulfed in its substance. The tube is therefore lengthened in a vertical direction to prevent this catastrophe and to maintain communication with the exterior. The process may continue until it is over an inch in length, the older part becoming closed up owing to the pressure of the growing sponge that surrounds it. Should the sponge die, the larva lives on in its tubes without suffering, and the ends of tubes containing larvæ may sometimes be found projecting from the worn surface of dead sponges. The larva does not eat the sponge but captures small insects by means of a pair of legs on the first segment of its thorax. In so doing it thrusts the anterior part of its body out of the tube, to the inner surface of which it adheres by means of the pair of false legs at the tip of the abdomen. This insect, which is usually found in the variety mollis, appears to do good to the sponge in two ways—by capturing other insects that might injure it and by giving support to its very feeble skeleton.

A precisely similar function, so far as the support of the sponge is concerned, is fulfilled by the tubular zoœcia of a phase of the polyzoon Plumatella fruticosa (see p. 218) which in India is more commonly found embedded in the substance of S. carteri than in that of any other species, although in Great Britain it is generally found in that of S. lacustris, which is there the commonest species of freshwater sponge.

Another animal that appears to play an active part in the œconomy of the sponge is a peculiar little worm (Chætogaster spongillæ) also found among the zoœcia of Plumatella and belonging to a widely distributed genus of which several species are found in association with pond-snails. Chætogaster spongillæ often occurs in enormous numbers in dead or dying sponges of S. carteri, apparently feeding on the decaying organic matter of the sponge and assisting by its movements in releasing numerous gemmules. In so doing it undoubtedly assists in the dissemination of the species.

Major J. Stephenson (Rec. Ind. Mus. v, p. 233) has recently found two other species of oligochætes inhabiting S. carteri var. lobosa from Travancore. Both these species, unlike Chætogaster spongillæ, belong to a genus that is vegetarian in habits. One of them, Nais pectinata, has not yet been found elsewhere, while the other, Nais communis, has a very wide distribution. The latter, however, occurs in the sponge in two forms—one with eyes, the other totally blind. The blind form (N. communis var. cæca) has only been found in this situation, but the other (var. punjabensis) lives free as well as in association with the sponge, in which the blind form was the commoner of the two.

The majority of the animals found in association with S. carteri gain shelter without evident assistance to the sponge. This is the case as regards the little fish (Gobius alcockii), one of the smallest of the vertebrates (length about 1/2 inch), which lays its eggs in the patent oscula, thus securing for them a situation peculiarly favourable to their development owing to the constant current of water that passes over them. In the absence of sponges, however, this fish attaches its eggs to the floating roots of the water-plant Pistia stratiotes. Numerous small crustacea[^[AE]] also take temporary or permanent refuge in the cavities of S. carteri, the most noteworthy among them being the Isopod Tachæa spongillicola[^[AF]], the adults of which are found in the canal of this and other sponges, while the young cling to the external surface of the carapace of Palæmon lamarrei and other small prawns. Many worms and insects of different kinds also enter the canals of S. carteri, especially when the sponge is becoming desiccated; from half-dry sponges numerous beetles and flies may be bred, notably the moth-fly Psychoda nigripennis[^[AG]] of which enormous numbers sometimes hatch out from such sponges.

As the sponge grows it frequently attaches itself to small molluscs such as the young of Vivipara bengalensis, which finally become buried in its substance and thus perish. Possibly their decaying bodies may afford it nourishment, but of the natural food of sponges we know little. S. carteri flourishes best and reaches its largest size in ponds used for domestic purposes by natives of India, and thrives in water thick with soap-suds. It is possible, though direct proof is lacking, that the sponge does good in purifying water used for washing the clothes, utensils, and persons of those who drink the same water, by absorbing decaying animal and vegetable matter from it.

Various minute algæ are found associated with S. carteri, but of these little is yet known. The green flush sometimes seen on the surface of the typical form is due to the fact that the superficial cells of the parenchyma contain green corpuscles. These, however, are never very numerous and are not found in the inner parts of the sponge, perhaps owing to its massive form. It is noteworthy that these green bodies flourish in large numbers throughout the substance of sponges of S. proliferens, a species always far from massive, growing in the same ponds as S. carteri.

9. Spongilla fragilis, Leidy.

Spongilla fragilis, Leidy, P. Ac. Philad. 1851, p. 278. Spongilla lordii, Bowerbank, P. Zool. Soc. London, 1863, p. 466, pl. xxxviii, fig. 17. Spongilla contecta, Noll, Zool. Garten*, 1870, p. 173. Spongilla ottavænsis, Dawson, Canad. Nat.* (new series) viii, p. 5 (1878). Spongilla sibirica, Dybowski, Zool. Anz., Jahr. i, p. 53 (1878). Spongilla morgiana, Potts, P. Ac. Philad. 1880, p. 330. Spongilla lordii, Carter, Ann. Nat. Hist. (5) vii, p. 89, pl. vi, fig. 13 (1881). Spongilla sibirica, Dybowski, Mém. Ac. St. Pétersb. (7) xxx, no. x, p. 10, fig. 12. Spongilla glomerata, Noll, Zool. Anz., Jahr. ix, p. 682 (1886). Spongilla fragilis, Vejdovsky, P. Ac. Philad. 1887, p. 176. Spongilla fragilis, Potts, ibid. p. 197, pl. v, fig. 2; pl. viii, figs. 1-4. Spongilla fragilis, Weltner, Arch. Naturg. lix (1), p. 266, pl. ix, figs. 18-20 (1893). Spongilla fragilis, id., Arch. Naturg. lxi (i), p. 117 (1895). Spongilla fragilis, id., in Semon's Zool. Forsch. in Austral. u. d. Malay. Arch. v, part v, p. 523. Spongilla fragilis, Annandale, P. U.S. Mus. xxxvii, p. 402 (1909). Spongilla fragilis, id., Annot. Zool. Japon. vii, part ii, p. 106, pl. ii, fig. 1 (1909).

Sponge flat, lichenoid, never of great thickness, devoid of branches, dense in texture but very friable; colour brown, green, or whitish; oscula numerous, small, flat, distinctly star-shaped.

Skeleton with well defined radiating and transverse fibres, which are never strong but form a fairly dense network with a small amount of spongin.

Spicules. Skeleton-spicules smooth, sharply pointed, moderately stout, as a rule nearly straight. No flesh-spicules. Gemmule-spicules cylindrical, blunt or abruptly pointed, nearly straight, covered with relatively stout, straight, irregular spines, which are equally distributed all over the spicule.

Gemmules bound together in free groups of varying numbers and forming a flat layer at the base of the sponge; each gemmule small in size, surrounded by a thick cellular coat of several layers; with a relatively long and stout foraminal tubule, which projects outwards through the cellular coat at the sides of the group or at the top of the basal layer of gemmules, is usually curved, and is not thickened at the tip; more than one foraminal tubule sometimes present on a single gemmule; gemmule-spicules arranged horizontally or at the base of the cellular coat.

The species as a species is easily distinguished from all others, its nearest ally being the N. American S. ingloriformis with sparsely spined skeleton-spicules which are very few in number, and gemmule groups in which the foraminal tubules all open downwards.

Several varieties of S. fragilis have been described in Europe and America.

Type.—Potts refers to the type as being in the Academy of Natural Sciences at Philadelphia.

Geographical Distribution.—All over Europe and N. America; also in Siberia, Australia, and S. America. The species is included in this work in order that its Asiatic local races may be fitly described.

9 a. Subsp. calcuttana*, nov.

? Spongilla decipiens, Weltner (partim), Arch. Naturg. lxi (i), pp. 117, 134 (1895). Spongilla decipiens, Annandale, Journ. As. Soc. Beng. 1906, p. 57. Spongilla fragilis, id., Rec. Ind. Mus. i, p. 390 (1907).

Fig. 15.—Spongilla fragilis subsp. calcuttana. A=group of gemmules, × 70; B=spicules, × 240. From type specimen.

This local race, which is common in Calcutta, is distinguished from the typical form mainly by the shape of its skeleton-spicules, most of which are abruptly pointed or almost rounded at the tips, sometimes bearing a minute conical projection at each end. The gemmule-spicules, which are usually numerous, are slender. The foraminal tubules are usually long and bent, but are sometimes very short and quite straight. The colour is usually greyish, occasionally brown.

I have not found this race except in Calcutta, in the ponds of which it grows on bricks or, very commonly, on the stems of bulrushes, often covering a considerable area.

Type in the Indian Museum.

9 b. Subsp. decipiens*, Weber.

Spongilla decipiens, Weber, Zool. Ergeb. Niederländ. Ost-Ind. i, p. 40, pl. iv, figs. 1-5 (1890).

This (?) local race is distinguished by the fact that the foraminal tubules are invariably short and straight and thickened at the tips, and that gemmule-spicules do not occur on the external surface of the cellular coat of the gemmules.

I include Weber's Spongilla decipiens in the Indian fauna on the authority of Weltner, who identified specimens from the Museum "tank," Calcutta, as belonging to this form. All, however, that I have examined from our "tank" belong to the subspecies calcuttana, most of the skeleton-spicules of which are much less sharp than those of decipiens. By the kindness of Prof. Max Weber I have been able to examine a co-type of his species, which is probably a local race peculiar to the Malay Archipelago.

Type in the Amsterdam Museum; a co-type in Calcutta.

Perhaps the Japanese form, which has spindle-shaped gemmule-spicules with comparatively short and regular spines, should be regarded as a third subspecies, and the Siberian form as a fourth.

10. Spongilla gemina*, sp. nov.

Sponge forming small, shallow, slightly dome-shaped patches of a more or less circular or oval outline, minutely hispid on the surface, friable but moderately hard. Oscula numerous but minute and inconspicuous, never star-shaped. Dermal membrane adhering closely to the sponge. Colour grey or brown.

Skeleton forming a close and regular network at the base of the sponge, becoming rather more diffuse towards the external surface; the radiating and the transverse fibres both well developed, of almost equal diameter. Little spongin present.

Spicules. Skeleton-spicules slender, smooth, sharply pointed. No flesh-spicules. Gemmule-spicules long, slender, cylindrical, blunt or bluntly pointed, somewhat irregularly covered with minute straight spines.

Gemmules small, bound together in pairs, as a rule free in the parenchyma but sometimes lightly attached at the base of the sponge. Each gemmule flattened on the surface by which it is attached to its twin, covered with a thin coat of polygonal air-spaces which contains two layers of gemmule-spicules crossing one another irregularly in a horizontal plane. One or two foraminal tubules present on the surface opposite the flat one, bending towards the latter, often of considerable length, cylindrical and moderately stout.

Type in the Indian Museum.

This species is closely allied to S. fragilis, from which it may be distinguished by the curious twinned arrangement of its gemmules. It also differs from S. fragilis in having extremely small and inconspicuous oscula.

Locality. I only know this sponge from the neighbourhood of Bangalore, where Dr. Morris Travers and I found it in October, 1910 growing on stones and on the leaves of branches that dipped into the water at the edge of a large tank.

11. Spongilla crassissima*, Annandale.

Spongilla crassissima, Annandale, J. Asiat. Soc. Bengal, 1907, p. 17, figs. 2, 3. Spongilla crassissima, id., ibid. p. 88. Spongilla crassissima, id., Rec. Ind. Mus. i. p. 390, pl. xiv, fig. 4 (1907).

Sponge very hard and strong, nearly black in colour, sometimes with a greenish tinge, forming spherical, spindle-shaped or irregular masses without branches but often several inches in diameter. Oscula circular or star-shaped, usually surrounded by radiating furrows; pores normally contained in single cells. External membrane closely adherent to the sponge except immediately round the oscula.

Skeleton dense, compact and only to be broken by the exercise of considerable force; radiating and transverse fibres not very stout but firmly bound together by spongin (fig. 6, p. 38), which occasionally extends between them as a delicate film; their network close and almost regular.

Spicules. Skeleton-spicules smooth, feebly curved, sausage-shaped but by no means short, as a rule bearing at each end a minute conical projection which contains the extremity of the axial filament. No flesh-spicules. Gemmule-spicules closely resembling those of S. fragilis subsp. calcuttana, but as a rule even more obtuse at the ends.

Gemmules as in S. fragilis subsp. calcuttana; a basal layer of gemmules rarely formed.

11 a. Var. crassior*, Annandale.

Spongilla crassior, Annandale, Rec. Ind. Mus. i, p. 389, pl. xiv, fig. 3 (1907).

This variety differs from the typical form chiefly in its even stronger skeleton (fig. 3, p. 33) and its stouter skeleton-spicules, which do not so often possess a terminal projection. The sponge is of a brownish colour and forms flat masses of little thickness but of considerable area on sticks and on the stems of water-plants.

Types.—The types of both forms are in the Indian Museum. Co-types have been sent to London.

Geographical Distribution.—This sponge is only known from Bengal. The variety crassior was found at Rajshahi (Rampur Bhulia) on the Ganges, about 150 miles N. of Calcutta, while the typical form is fairly common in the "tanks" of Calcutta and very abundant in the Sur Lake near Puri in Orissa.

Fig. 16.—Spicules of Spongilla crassissima var. crassior (from type specimen), × 240.

Biology.—S. crassissima is usually found near the surface in shallow water. Attached to the roots of the floating water-plant Pistia stratiotes it assumes a spherical form, while on sticks or like objects it is spindle-shaped. Sometimes it is found growing on the same stick or reed-stem as S. carteri, the two species being in close contact and S. carteri always overlapping S. crassissima. The dark colour is due to minute masses of blackish pigment in the cells of the parenchyma. The dense structure of the sponge is not favourable to the presence of incolæ, but young colonies of the polyzoon Plumatella fruticosa are sometimes overgrown by it. Although they may persist for a time by elongating their tubular zoœcia through the substance of the sponge, they do not in these circumstances reach the same development as when they are overgrown by the much softer S. carteri.

S. crassissima is found during the "rains" and the cold weather. In Calcutta it attains its maximum size towards the end of the latter season. In spite of its hard and compact skeleton, the sponge does not persist from one cold weather to another.

A curious phenomenon has been noticed in this species, but only in the case of sponges living in an aquarium, viz. the cessation during the heat of the day of the currents produced by its flagella.

Subgenus C. STRATOSPONGILLA, Annandale.

Stratospongilla, Annandale, Zool. Jahrb., Syst. xxvii, p. 561 (1909).

Type, Spongilla bombayensis, Carter.

Spongillæ in the gemmules of which the pneumatic layer is absent or irregularly developed, its place being sometimes taken by air-spaces between the stout chitinous membranes that cover the gemmule. At least one of these membranes is always present.

The gemmule-spicules lie in the membrane or membranes parallel to the surface of the gemmule, and are often so arranged as to resemble a mosaic. The gemmules themselves are usually adherent to the support of the sponge. The chitinous membrane or membranes are often in continuity with a membrane that underlies the base of the sponge. The skeleton is usually stout, though often almost amorphous, and the skeleton-spicules are sometimes sausage-shaped.

Sponges of this subgenus form crusts or sheets on solid submerged objects.

Stratospongilla is essentially a tropical subgenus, having its head-quarters in Central Africa and Western India. One of its species, however, (S. sumatrana*, Weber) occurs both in Africa and the Malay Archipelago, while another has only been found in S. America (S. navicella, Carter).

Aberrant species occur in China (S. sinensis*, S. coggini*) and the Philippines (S. clementis*). Three species have been found in the Bombay Presidency and Travancore, one of which (S. bombayensis*) extends its range eastwards to Mysore and westwards across the Indian Ocean to Natal.

12. Spongilla indica*, Annandale.

Spongilla indica, Annandale, Rec. Ind. Mus. ii, p. 25, figs. 1, 2 (1908).

Sponge forming a very thin layer, of a bright green or pale grey colour; surface smooth, minutely hispid; pores and oscula inconspicuous, the latter approached in some instances by radiating furrows; subdermal cavity small; texture compact, rather hard.

Skeleton incoherent, somewhat massive owing to the large number of spicules present. Spicules forming triangular meshes and occasionally arranged in vertical lines several spicules broad but without spongin.

Spicules. Skeleton-spicules straight or nearly straight, slender, cylindrical, amphistrongylous, uniformly covered with minute, sharp spines; flesh-spicules slender, sharply pointed, straight or curved, irregularly covered with relatively long, straight sharp spines, abundant in the dermal membrane, scarce in the substance of the sponge. Gemmule-spicules short, stout, sausage-shaped, covered with minute spines, which are sometimes absent from the extremities.

Gemmules spherical, somewhat variable in size, with a single aperture, which is provided with a trumpet-shaped foraminal tubule and is situated at one side of the gemmule in its natural position; the inner chitinous coat devoid of spicules, closely covered by an outer coat composed of a darkly coloured chitinoid substance in which the gemmule-spicules are embedded, lying parallel or almost parallel to the inner coat. The outer coat forms a kind of mantle by means of the skirts of which the gemmule is fastened to the support of the sponge. This coat is pierced by the foraminal tubule. The gemmules are distinct from one another.

Fig. 17.—Gemmule of Spongilla indica seen from the side (from type specimen), magnified.

S. indica is closely allied to S. sumatrana*, Weber, which has been found both in the Malay Archipelago and in East Africa. It may be distinguished by its blunt, almost truncated megascleres and comparatively slender gemmule-spicules.

Type in the Indian Museum.

Habitat, etc.—Growing, together with S. cinerea and Corvospongilla lapidosa, on the stone sides of an artificial conduit in the R. Godaveri at Nasik on the eastern side of the Western Ghats in the Bombay Presidency. The water was extremely dirty and was used for bathing purposes. The sponge was green where the light fell upon it, grey where it was in the shadow of the bridge under which the conduit ran. The only specimens I have seen were taken in November, 1907.

13. Spongilla bombayensis*, Carter. ([Plate II], fig. 2.)

Spongilla bombayensis, Carter, Ann. Nat. Hist. (5) x, p. 369, pl. xvi, figs. 1-6 (1882). Spongilla bombayensis, Annandale, Zool. Jahrb., Syst. xxvii, p. 562, figs. B, C (1909).

Sponge hard but friable, forming thin layers or cushions; its surface often irregular but without a trace of branches; its area never very great; oscula inconspicuous; external membrane adhering closely to the sponge; colour brownish or greyish.

Fig. 18.—Gemmule of Spongilla bombayensis as seen from above (from type specimen), magnified.

Skeleton almost amorphous, very dense, consisting of large numbers of spicules arranged irregularly; radiating fibres occasionally visible in sections, but almost devoid of spongin; a more or less definite reticulation of horizontal spicules lying immediately under the external membrane.

Spicules. Skeleton-spicules slender, pointed, feebly curved, irregularly roughened or minutely spined all over the surface. Flesh-spicules straight, narrowly rhomboidal in outline, sharply pointed, slender, covered with minute, irregular, straight spines, scanty in the parenchyma, abundant in the external membrane. Gemmule-spicules sausage-shaped or bluntly pointed, variable in length but usually rather stout, covered with minute spines, as a rule distinctly curved.

Gemmules round or oval, firmly adherent[^[AH]] to the base of the sponge, as a rule rather shallowly dome-shaped, covered by two thick chitinous membranes, in each of which there is a dense horizontal layer of spicules; no granular or cellular covering; the two chitinous coats separated by an empty space; the aperture or apertures on the side of the gemmule in its natural position, provided with foraminal tubules, which may be either straight or curved, project through the outer chitinous membrane and often bend down towards the base of the gemmule. The spicules of the outer layer often more irregular in outline and less blunt than those of the inner layer.

This sponge is allied to S. indica, but is distinguished among other characters by its sharp skeleton-spicules and by the fact that the gemmule is covered by two chitinous membranes instead of one.

Type in the British Museum; a fragment in the Indian Museum.

Geographical Distribution.—S. and W. India and S. Africa. Carter's type was found in the island of Bombay, my own specimens in Igatpuri Lake in the Western Ghats. I have recently (October 1910) found sponges and bare gemmules attached to stones at the end of a tank about 10 miles from Bangalore (Mysore State) in the centre of the Madras Presidency. Prof. Max Weber obtained specimens in Natal.

Biology.—The specimens collected by Prof. Weber in Natal and those collected by myself in the Bombay Presidency were both obtained in the month of November. It is therefore very interesting to compare them from a biological point of view. In so doing, it must be remembered that while in S. Africa November is near the beginning of summer, in India it is at the beginning of the "cold weather," that is to say, both the coolest and the driest season of the year. The lake in which my specimens were obtained had, at the time when they were collected, already sunk some inches below its highest level, leaving bare a gently sloping bank of small stones. Adhering to the lower surface of these stones I found many small patches of Spongilla bombayensis, quite dry but complete so far as their harder parts were concerned and with the gemmules fully formed at their base. From the shallow water at the edge of the lake I took many similar stones which still remained submerged. It was evident that the sponge had been just as abundant on their lower surface as on that of the stones which were now dry; but only the gemmules remained, sometimes with a few skeleton-spicules adhering to them (Pl. II, fig. 2). The bulk of the skeleton had fallen away and the parenchyma had wholly perished. In a few instances a small sponge, one or two millimetres in diameter, had already been formed among the gemmules; but these young sponges appeared to belong to some other species, possibly Spongilla indica, which was also common in the lake.

Carter's specimen of S. bombayensis, which was evidently in much the same condition as those I found still submerged a month later, was taken in October in a disused quarry. It was surrounded by a mass of S. carteri three inches in diameter, and was attached to a herbaceous annual. The point on the edge of the quarry at which this plant grew was not reached by the water until July. It is therefore necessary to assume that the gemmules of S. bombayensis had been formed between July and October. Probably the larva of the sponge had settled down on the plant during the "rains"—which commence in Bombay about the beginning of June—and had grown rapidly. The production of gemmules may have been brought about owing to the sponge being choked by the more vigorous growth of S. carteri, a species which grows to a considerable size in a comparatively short time, while S. bombayensis apparently never reaches a thickness of more than a few millimetres.

The manner in which the gemmules of S. bombayensis are fastened to the solid support of the sponge must be particularly useful in enabling them to sprout in a convenient environment as soon as the water reaches them. The fact that the gemmules remained fixed without support renders it unnecessary for the skeleton to persist as a cage containing them (or at any rate a proportion of them) during the period of rest.

Prof. Weber's specimens of S. bombayensis were collected in a river, apparently on stones or rocks, towards the beginning of the S. African summer. They contain comparatively few gemmules and were evidently in a vigorous condition as regards vegetative growth. Unfortunately we know nothing of the seasonal changes which take place in freshwater sponges in S. Africa, but the difference between these changes in Europe and in India shows that they are dependent on environment as well as the idiosyncrasy of the species. It is very interesting, therefore, to see that the condition of sponges taken in S. Africa differs so widely from that of other individuals of the same species taken in India at the same season.

In Prof. Weber's specimens I have found numerous small tubules of inorganic débris. These appear to be the work of Chironomid larvæ, of which there are several specimens loose in the bottle containing the sponges. Other tubules of a very similar appearance but with a delicate chitinoid foundation appear to be the remains of a species of Plumatella of which they occasionally contain a statoblast.

14. Spongilla ultima*, Annandale. ([Plate II], fig. 3.)

Spongilla ultima, Annandale, Rec. Ind. Mus. v, p. 31 (1910).

Sponge hard and strong, forming a thin layer on solid objects, of a pale green colour (dry); the oscula small but rendered conspicuous by the deep radiating furrows that surround them; external surface of the sponge rough but not spiny.

Skeleton forming a compact but somewhat irregular reticulation in which the radiating fibres are not very much more distinct than the transverse ones; a considerable amount of almost colourless spongin present.

Spicules. Skeleton-spicules smooth, stout, amphioxous, as a rule straight or nearly straight, not infrequently inflated in the middle or otherwise irregular. No flesh-spicules. Gemmule-spicules variable in size, belonging to practically every type and exhibiting practically every abnormality possible in the genus, the majority being more or less sausage-shaped and having a roughened surface, but others being cruciform, spherical, subspherical, rosette-like, needle-like, bifid or even trifid at one extremity.

Fig. 19.—Spicules of Spongilla ultima (from type specimen), × 120.

Gemmules adherent, spherical, large, each covered by two distinct layers of horizontal spicules; the outer layer intermixed with skeleton-spicules and often containing relatively large siliceous spheres, a large proportion of the spicules being irregular in shape; the spicules of the inner layer much more regular and as a rule sausage-shaped. The outer layer is contained in a chitinous membrane which spreads out over the base of the sponge. The foraminal tubules are short and straight.

This sponge is allied to S. bombayensis, from which it is distinguished not only by the abnormal characters of its gemmule-spicules and the absence of flesh-spicules, but also by the form of its skeleton-spicules and the structure of its skeleton. I have examined several specimens dry and in spirit; but S. ultima is the only Indian freshwater sponge, except Corvospongilla burmanica, I have not seen in a fresh condition.

Types in the Indian Museum; co-types at Trivandrum.

Habitat. Discovered by Mr. R. Shunkara Narayana Pillay, of the Trivandrum Museum, in a tank near Cape Comorin, the southernmost point of the Indian Peninsula.

Genus 2. PECTISPONGILLA, Annandale.

Pectispongilla, Annandale, Rec. Ind. Mus. iii, p. 103 (1909).

Type, Pectispongilla aurea, Annandale.

The structure of the sponge resembling that of Euspongilla or Ephydatia; but the gemmule-spicules bear at either end, at one side only, a double vertical row of spines, so that they appear when viewed in profile like a couple of combs joined together by a smooth bar.

Fig. 20.—Gemmule and spicules of Pectispongilla aurea (type specimen). a, Skeleton-spicules; b, gemmule-spicules; b', a single gemmule-spicule more highly magnified.

Geographical Distribution.—The genus is monotypic and is only known from Travancore and Cochin in the south-west of the Indian Peninsula.

15. Pectispongilla aurea*, Annandale.

Pectispongilla aurea, Annandale, op. cit., p. 103, pl. xii, fig. 2.

Sponge forming minute, soft, cushion-like masses of a deep golden colour (dull yellow in spirit); the surface smooth, minutely hispid. One relatively large depressed osculum usually present in each sponge; pores inconspicuous; dermal membrane in close contact with the parenchyma.

Skeleton consisting of slender and feebly coherent radiating fibres as a rule two or three spicules thick, with single spicules or ill-defined transverse fibres running horizontally. Towards the external surface transverse spicules are numerous, but they do not form any very regular structure.

Spicules. Skeleton-spicules smooth, sharply pointed, straight or nearly so. Gemmule-spicules minute, with the stem smooth and cylindrical, relatively stout and much longer than the comb at either end; the two combs equal, with a number of minute, irregularly scattered spines between the two outer rows of stouter ones. No free microscleres.

Gemmules minute, spherical, with a single aperture, which is provided with a very short foraminal tubule; the granular coat well developed; the spicules arranged in a slanting position, but more nearly vertically than horizontally, with the combs pointing in all directions; no external chitinous membrane.

The gemmule-spicules first appear as minute, smooth, needle-like bodies, which later become roughened on one side at either end and so finally assume the mature form. There are no bubble-cells in the parenchyma.

15a. Var. subspinosa*, nov.

This variety differs from the typical form in having its skeleton spicules covered with minute irregular spines or conical projections.

Types of both the typical form and the variety in the Indian Museum; co-types of the typical form in the Trivandrum Museum.

Geographical Distribution.—The same as that of the genus. Localities:—Tenmalai, at the base of the western slopes of the W. Ghats in Travancore (typical form) (Annandale); Ernakulam and Trichur in Cochin (var. subspinosa) (G. Mathai).

Biology.—My specimens, which were taken in November, were growing on the roots of trees at the edge of an artificial pool by the roadside. They were in rather dense shade, but their brilliant golden colour made them conspicuous objects in spite of their small size. Mr. Mathai's specimens from Cochin were attached to water-weeds and to the husk of a cocoanut that had fallen or been thrown into the water.

Genus 3. EPHYDATIA, Lamouroux.

Ephydatia, Lamouroux, Hist. des Polyp. corall. flex.* p. 6 (fide Weltner) (1816). Ephydatia, J. E. Gray, P. Zool. Soc. London. 1867, p. 550. Trachyspongilla, Dybowsky (partim), Zool. Anz. i, p. 53 (1874). Meyenia, Carter (partim), Ann. Nat. Hist. (5) vii, p. 90 (1881). Carterella, Potts & Mills (partim), P. Ac. Philad. 1881, p. 150. Ephydatia, Vejdovsky, Abh. Böhm. Ges. xii, p. 23 (1883). Meyenia, Potts (partim), ibid. 1887, p. 210. Carterella, id. (partim), ibid. 1887, p. 260. Ephydatia, Weltner (partim), Arch. Naturg. lxi (i), p. 121 (1895). Ephydatia, Annandale, P. U.S. Mus. xxxvii, p. 404 (1909).

Type, (?) Spongilla fluviatilis, auctorum.

This genus is separated from Spongilla by the structure of the gemmule-spicules, which bear at either end a transverse disk with serrated or deeply notched edges, or at any rate with edges that are distinctly undulated. The disks are equal and similar. True flesh-spicules are usually absent, but more or less perfect birotulates exactly similar to those associated with the gemmules are often found free in the parenchyma. The skeleton is never very stout and the skeleton-spicules are usually slender.

As has been already stated, some authors consider Ephydatia as the type-genus of a subfamily distinguished from the subfamily of which Spongilla is the type-genus by having rotulate gemmule-spicules. The transition between the two genera, however, is a very easy one. Many species of the subgenus Euspongilla, the typical subgenus of Spongilla (including S. lacustris, the type-species of the genus), have the spines at the ends of the gemmule-spicules arranged in such a way as to suggest rudimentary rotules, while in the typical form of S. crateriformis this formation is so distinct that the species has hitherto been placed in the genus Ephydatia (Meyenia), although in some sponges that agree otherwise with the typical form of the species the gemmule-spicules are certainly not rotulate and in none do these spicules bear definite disks.

Geographical Distribution.—Ephydatia, except Spongilla, is the most generally distributed genus of the Spongillidæ, but in most countries it is not prolific in species. In Japan, however, it appears to predominate over Spongilla. Only one species is known from India, but another (E. blembingia*, Evans) has been described from the Malay Peninsula, while Weber found both the Indian species and a third (E. bogorensis*) in the Malay Archipelago.

16. Ephydatia meyeni* (Carter).

Spongilla meyeni, Carter, J. Bomb. Asiat. Soc. iii, p. 33, pl. i, fig. 1, & Ann. Nat. Hist. (2) iv, p. 84, pl. iii, fig. 1 (1849). Spongilla meyeni, Bowerbank, P. Zool. Soc. London, 1863, p. 448, pl. xxxviii, fig. 4. Spongilla meyeni, Carter, Ann. Nat. Hist. (5) vii, p. 93 (1881). Ephydatia fluviatilis, Weber, Zool. Ergeb. Niederländ. Ost-Ind. i. pp. 32, 46 (1890). Ephydatia mülleri, Weltner (partim), Arch. Naturg. lxi (i), p. 125 (1895). Ephydatia robusta, Annandale, J. Asiat. Soc. Bengal, 1907, p. 24, fig. 7. Ephydatia mülleri subsp. meyeni, id., Rec. Ind. Mus. ii, p. 306 (1908).

Sponge hard and firm but easily torn, usually of a clear white, sometimes tinged with green, forming irregular sheets or masses never of great thickness, without branches but often with stout subquadrate projections, the summits of which are marked with radiating grooves; the whole surface often irregularly nodulose and deeply pitted; the oscula inconspicuous; the membrane adhering closely to the parenchyma. The parenchyma contains numerous bubble-cells (see p. 31, fig. 2).

Skeleton dense but by no means regular; the radiating fibres distinct and containing a considerable amount of spongin, at any rate in the outer part of the sponge; transverse fibres hardly distinguishable, single spicules and irregular bundles of spicules taking their place.

Fig. 21.—Gemmule and spicules of Ephydatia meyeni (from Calcutta).
a, Skeleton-spicules; b, gemmule-spicules.

Spicules. Skeleton-spicules entirely smooth, moderately stout, feebly curved, sharply pointed. No flesh-spicules. Gemmule-spicules with the shaft as a rule moderately stout, much longer than the diameter of one disk, smooth or with a few stout, straight horizontal spines, which are frequently bifid or trifid; the disks flat, of considerable size, with their margins cleanly and deeply divided into a comparatively small number of deep, slender, triangular processes of different sizes; the shaft extending not at all or very little beyond the disks.

Gemmules spherical, usually numerous and of rather large size; each covered by a thick layer of minute air-spaces, among which the gemmule-spicules are arranged vertically, often in two or even three concentric series; a single short foraminal tubule; the pneumatic coat confined externally by a delicate membrane, with small funnel-shaped pits over the spicules of the outer series.

I think that the gemmules found by me in Bhim Tal and assigned to Potts's Meyenia robusta belong to this species, but some of the spicules are barely as long as the diameter of the disks. In any case Potts's description is so short that the status of his species is doubtful. His specimens were from N. America.

E. meyeni is closely related to the two commonest Holarctic species of the genus, E. fluviatilis and E. mülleri, which have been confused by several authors including Potts. From E. fluviatilis it is distinguished by the possession of bubble-cells in the parenchyma, and from E. mülleri by its invariably smooth skeleton-spicules and the relatively long shafts of its gemmule-spicules. The latter character is a marked feature of the specimens from the Malay Archipelago assigned by Prof. Max Weber to E. fluviatilis; I am indebted to his kindness for an opportunity of examining some of them.

Type in the British Museum; a fragment in the Indian Museum.

Geographical Distribution.—India and Sumatra. Localities:—Bengal, Calcutta and neighbourhood (Annandale); Madras Presidency, Cape Comorin, Travancore (Trivandrum Mus.): Bombay Presidency, Island of Bombay (Carter): Himalayas, Bhim Tal, Kumaon (alt. 4,500 feet) (Annandale).

Biology.—My experience agrees with Carter's, that this species is never found on floating objects but always on stones or brickwork. It grows in the Calcutta "tanks" on artificial stonework at the edge of the water, together with Spongilla carteri, S. alba, S. fragilis subsp. calcuttana, and Trochospongilla latouchiana. It flourishes during the cold weather and often occupies the same position in succeeding years. In this event the sponge usually consists of a dead base, which is of a dark brownish colour and contains no cells, and a living upper layer of a whitish colour.

The larva of Sisyra indica is sometimes found in the canals, but the close texture of the sponge does not encourage the visits of other incolæ.

Genus 4. DOSILIA, Gray.

Dosilia, J. E. Gray, P. Zool. Soc. London, 1867, p. 550.

Type, Spongilla plumosa, Carter.

This genus is distinguished from Ephydatia by the nature of the free microscleres, the microscleres of the gemmule being similar in the two genera. The free microscleres consist as a rule of several or many shafts meeting together in several or many planes at a common centre, which is usually nodular. The free ends of these shafts often possess rudimentary rotulæ. Occasionally a free microsclere may be found that is a true monaxon and sometimes such spicules are more or less distinctly birotulate. The skeleton is also characteristic. It consists mainly of radiating fibres which bifurcate frequently in such a way that a bush-like structure is produced. Transverse fibres are very feebly developed and are invisible to the naked eye. Owing to the structure of the skeleton the sponge has a feathery appearance.

Gray originally applied the name Dosilia to this species and to "Spongilla" baileyi, Bowerbank. It is doubtful how far his generic description applies to the latter, which I have not seen; but although the position of "Spongilla" baileyi need not be discussed here, I may say that I do not regard it as a congener of Dosilia plumosa, the free microscleres of which are of a nature rare but not unique in the family. With Dosilia plumosa we must, in any case, associate in one genus the two forms that have been described as varieties, viz., palmeri*, Potts from Texas and Mexico, and brouini*, Kirkpatrick from the White Nile. By the kindness of the authorities of the Smithsonian Institution and the British Museum I have been able to examine specimens of all three forms, in each case identified by the author of the name, and I am inclined to regard them as three very closely allied but distinct species. Species with free microscleres similar to those of these three forms but with heterogeneous or tubelliform gemmule-spicules will probably need the creation of a new genus or new genera for their reception.

Geographical Distribution.—The typical species occurs in Bombay and Madras; D. palmeri has probably an extensive range in the drier parts of Mexico and the neighbouring States, while D. brouini has only been found on the banks of the White Nile above Khartoum, in Tropical Africa.

17. Dosilia plumosa* (Carter).

Spongilla plumosa, Carter, J. Bomb. Asiat. Soc. iii, p. 34, pl. i, fig. 2, & Ann. Nat. Hist. (2) iv, p. 85, pl. iii, fig. 2 (1849). Spongilla plumosa, Bowerbank, P. Zool. Soc. London, 1863, p. 449, pl. xxxviii, fig. 5. Dosilia plumosa, J. E. Gray, ibid. 1867, p. 551. Meyenia plumosa, Carter, Ann. Nat. Hist. (5) vii, p. 94, pl. v, fig. 6 (1881). Meyenia plumosa, Potts, P. Ac. Philad. 1887, p. 233. Ephydatia plumosa, Weltner, Arch. Naturg. lxi (i), p. 126 (1895). Ephydatia plumosa, Petr, Rozp. Ceske Ak. Praze, Trída ii, pl. ii, figs. 29, 30 (text in Czech) (1899).

Sponge forming soft irregular masses which are sometimes as much as 14 cm. in diameter, of a pale brown or brilliant green colour; no branches developed but the surface covered with irregular projections usually of a lobe-like nature.

Skeleton delicate, with the branches diverging widely, exhibiting the characteristic structure of the genus in a marked degree, containing a considerable amount of chitin, which renders it resistant in spite of its delicacy.

Spicules. Skeleton-spicules smooth, sharply pointed, nearly straight, moderately slender, about twenty times as long as their greatest transverse diameter. Flesh-spicules occasionally amphioxous or birotulate and with a single shaft, more frequently consisting of many shafts meeting in a distinct central nodule, which is itself smooth; the shafts irregularly spiny, usually more or less nodular at the tip, which often bears a distinct circle of recurved spines that give it a rotulate appearance. Gemmule-spicules with long, slender, straight shafts, which bear short, slender, straight, horizontal spines sparsely and irregularly scattered over their surface; the rotulæ distinctly convex when seen in profile; their edge irregularly and by no means deeply notched; the shafts not extending beyond their surface but clearly seen from above as circular umbones.

Fig. 22.—Dosilia plumosa.

A=microscleres, × 240; B=gemmule as seen in optical section from below, × 75. (From Rambha.)

Gemmules. Somewhat depressed, covered with a thick granular pneumatic coat, in which the spicules stand erect; the single aperture depressed. Each gemmule surrounded more or less distinctly by a circle or several circles of flesh-spicules.

Type in the British Museum; some fragments in the Indian Museum.

Geographical Distribution.—Bombay and Madras. Carter's specimens were taken in the island of Bombay, mine at Rambha in the north-east of the Madras Presidency. I have been unable to discover this species in the neighbourhood of Calcutta, but it is apparently rare wherever it occurs.

Biology.—Carter writes as regards this species:—"This is the coarsest and most resistant of all the species. As yet I have only found three or four specimens of it, and these only in two tanks. I have never seen it fixed on any solid body, but always floating on the surface of the water, about a month after the first heavy rains of the S.W. monsoon have fallen. Having made its appearance in that position, and having remained there for upwards of a month, it then sinks to the bottom. That it grows like the rest, adherent to the sides of the tank, must be inferred from the first specimen which I found (which exceeds two feet in circumference) having had a free and a fixed surface, the latter coloured by the red gravel on which it had grown. I have noticed it growing, for two successive years in the month of July, on the surface of the water of one of the two tanks in which I have found it, and would account for its temporary appearance in that position, in the following way, viz., that soon after the first rains have fallen, and the tanks have become filled, all the sponges in them appear to undergo a partial state of putrescency, during which gas is generated in them, and accumulates in globules in their structure, through which it must burst, or tear them from their attachments and force them to the surface of the water. Since then the coarse structure of plumosa would appear to offer greater resistance to the escape of this air, than that of any of the other species, it is probable that this is the reason of my having hitherto only found it in the position mentioned."

It seems to me more probable that the sponges are actually broken away from their supports by the violence of the rain and retain air mechanically in their cavities. The only specimens of D. plumosa that I have seen alive were attached very loosely to their support. In writing of the "coarse structure" of this species, Carter evidently alludes to the wide interspaces between the component branches of the skeleton.

My specimens were attached to the stem of a water-lily growing in a pool of slightly brackish water and were of a brilliant green colour. I mistook them at first for specimens of S. lacustris subsp. reticulata in which the branches had not developed normally. They were taken in March and were full of gemmules. The pool in which they were growing had already begun to dry up.

Genus 5. TROCHOSPONGILLA, Vejdovsky.

Trochospongilla, Vejdovsky, Abh. K. Böhm. Ges. Wiss. xii, p. 31 (1883). Trochospongilla, Wierzejski, Arch. Slaves de Biologie, i, p. 44 (1886). Trochospongilla, Vejdovsky, P. Ac. Philad. 1887, p. 176. Meyenia, Potts (partim), ibid. p. 210. Tubella, id. (partim), ibid., p. 248. Meyenia, Carter (partim), Ann. Nat. Hist. (5) vii, p. 90 (1881). Trochospongilla, Weltner, in Zacharias's Tier- und Pflanzenwelt, i, p. 215 (1891). Trochospongilla, id., Arch. Naturg. lxi (i), p. 120 (1895). Tubella, id. (partim), ibid. p. 128.

Type, Spongilla erinaceus, Ehrenberg.

The characteristic feature of this genus is that the rotulæ of the gemmule-spicules, which are homogeneous, have smooth instead of serrated edges. Their stem is always short and they are usually embedded in a granular pneumatic coat. The sponge is small in most of the species as yet known; in some species microscleres without rotulæ are associated with the gemmules.

Fig. 23.—A=skeleton-spicule of Trochospongilla latouchiana; A'=gemmule-spicule of the same species; B=gemmule of T. phillottiana as seen in optical section from above; B'=skeleton-spicule of same species: A, A', B' × 240; B × 75. All specimens from Calcutta.

I think it best to include in this genus, as the original diagnosis would suggest, all those species in which all the gemmule-spicules are definitely birotulate and have smooth edges to their disks, confining the name Tubella to those in which the upper rotula is reduced to a mere knob. Even in those species in which the two disks are normally equal, individual spicules may be found in which the equality is only approximate, while, on the other hand, it is by no means uncommon for individual spicules in such species as "Tubella" pennsylvanica, which is here included in Trochospongilla, to have the two disks nearly equal, although normally the upper one is much smaller than the lower. There is very rarely any difficulty, however, in seeing at a glance whether the edge of the disk is smooth or serrated, the only species in which this difficulty would arise being, so far as I am aware, the Australian Ephydatia capewelli* (Haswell), the disks of which are undulated and nodulose rather than serrated.

Geographical Distribution.—The genus includes so large a proportion of small, inconspicuous species that its distribution is probably known but imperfectly. It would seem to have its headquarters in N. America but also occurs in Europe and Asia. In India three species have been found, one of which (T. pennsylvanica) has an extraordinarily wide and apparently discontinuous range, being common in N. America, and having been found in the west of Ireland, the Inner Hebrides, and near the west coast of S. India. The other two Indian species are apparently of not uncommon occurrence in eastern India and Burma.

Key to the Indian Species of Trochospongilla.

18. Trochospongilla latouchiana*, Annandale.

Trochospongilla latouchiana, Annandale, J. Asiat. Soc. Bengal, 1907, p. 21, fig. 5. Trochospongilla latouchiana, id., Rec. Ind. Mus. ii, p. 157 (1908). Trochospongilla leidyi, id. (nec Bowerbank), ibid. iii, p. 103 (1909).

Fig. 24.—Trochospongilla latouchiana.

Vertical section of part of skeleton with gemmules in situ, × 30; also a single gemmule, × 70. (From Calcutta).

Sponge forming cushion-shaped masses rarely more than a few centimetres in diameter or thickness and of a brown or yellow colour, hard but rather brittle; surface evenly rounded, minutely hispid; oscula inconspicuous, small, circular, depressed, very few in number; external membrane adhering closely to the parenchyma; a chitinous membrane at the base of the sponge. Larger sponges divided into several layers by similar membranes.

Skeleton dense, forming a close reticulation; radiating fibres slender but quite distinct, running up right through the sponge, crossed at frequent intervals by single spicules or groups of spicules.

Spicules. Skeleton-spicules smooth, about twenty times as long as the greatest transverse diameter, as a rule sharply pointed; smooth amphistrongyli, which are often inflated in the middle, sometimes mixed with them but never in large numbers. No flesh-spicules. Gemmule-spicules with the rotulæ circular or slightly asymmetrical, flat or nearly flat, marked with a distinct double circle as seen from above, sometimes not quite equal; the shaft not projecting beyond them; the diameter of the rotule 4-1/2 to 5 times that of the shaft, which is about 2-2/3 times as long as broad.

Gemmules small (0.2 × 0.18 mm.), as a rule very numerous and scattered throughout the sponge, flask-shaped, clothed when mature with a thin microcell coat in which the birotulates are arranged with overlapping rotulæ, their outer rotulæ level with the surface; foraminal aperture circular, situated on an eminence.

Average Measurements.

T. latouchiana is closely related to T. leidyi (Bowerbank) from N. America, but is distinguished by its much more slender skeleton-spicules, by the fact that the gemmules are not enclosed in cages of megascleres or confined to the base of the sponge, and by differences in the structure of the skeleton.

Type in the Indian Museum.

Geographical Distribution.—Lower Bengal and Lower Burma. Localities:—Bengal, Calcutta and neighbourhood (Annandale): Burma, Kawkareik, Amherst district, Tenasserim (Annandale).

Biology.—This species, which is common in the Museum tank, Calcutta, is apparently one of those that can grow at any time of year, provided that it is well covered with water. Like T. leidyi it is capable of producing fresh layers of living sponge on the top of old ones, from which they are separated by a chitinous membrane. These layers are not, however, necessarily produced in different seasons, for it is often clear from the nature of the object to which the sponge is attached that they must all have been produced in a short space of time. What appears to happen in most cases is this:—A young sponge grows on a brick, the stem of a reed or some other object at or near the edge of a pond, the water in which commences to dry up. As the sponge becomes desiccated its cells perish. Its gemmules are, however, retained in the close-meshed skeleton, which persists without change of form. A heavy shower of rain then falls, and the water rises again over the dried sponge. The gemmules germinate immediately and their contents spread out over the old skeleton, secrete a chitinous membrane and begin to build up a new sponge. The process may be repeated several times at the change of the seasons or even during the hot weather, or after a "break in the rains." If, however, the dried sponge remains exposed to wind and rain for more than a few months, it begins to disintegrate and its gemmules are carried away to other places. Owing to their thin pneumatic coat and relatively heavy spicules they are not very buoyant. Even in the most favourable circumstances the sponge of T. latouchiana never forms sheets of great area. In spite of its rapid growth it is frequently overgrown by Spongilla carteri.

19. Trochospongilla phillottiana*, Annandale.

Trochospongilla phillottiana, Annandale, J. Asiat. Soc. Bengal, 1907, p. 22, fig. 6. Trochospongilla phillottiana, id., Rec. Ind. Mus. i, p. 269 (1907). Trochospongilla phillottiana, id., ibid. ii, p. 157 (1908).

Sponge hard but friable, forming sheets or patches often of great extent but never more than about 5 mm. thick; the surface minutely hispid, flat; colour pale yellow, the golden-yellow gemmules shining through the sponge in a very conspicuous manner; oscula inconspicuous; external membrane adherent; no basal chitinous membrane.

Skeleton dense but by no means strong; the reticulation close but produced mainly by single spicules, which form triangular meshes; radiating fibres never very distinct, only persisting for a short distance in a vertical direction; each gemmule enclosed in an open, irregular cage of skeleton-spicules.

Spicules. Skeleton-spicules short, slender, blunt, more or less regularly and strongly spiny, straight or feebly curved. No flesh-spicules. Gemmule-spicules with the rotulæ circular, very wide as compared with the shaft, concave on the surface, with the shaft projecting as an umbo on the surface; the lower rotula often a little larger than the upper.

Gemmules numerous, situated at the base of the sponge in irregular, one-layered patches, small (0.32 × 0.264 mm.), of a brilliant golden colour, distinctly wider than high, with a single aperture situated on an eminence on the apex, each clothed (when mature) with a pneumatic coat that contains relatively large but irregular air-spaces among which the spicules stand with the rotulæ overlapping alternately, a funnel-shaped pit in the coat descending from the surface to the upper rotula of each of them; the surface of the gemmule covered with irregular projections.

This species appears to be related to T. pennsylvanica, from which it differs mainly in the form of its gemmule-spicules and the structure of its gemmule. My original description was based on specimens in which the gemmule-spicules were not quite mature.

Type in the Indian Museum.

Geographical Distribution.—Lower Bengal and Lower Burma. Localities:—Bengal, Calcutta (Annandale): Burma, jungle pool near Kawkareik, Amherst district, Tenasserim (Annandale).

Biology.—This species covers a brick wall at the edge of the Museum tank in Calcutta every year during the "rains." In the cold weather the wall is left dry, but it is usually submerged to a depth of several feet before the middle of July. It is then rapidly covered by a thin layer of the sponge, which dies down as soon as the water begins to sink when the "rains" are over. For some months the gemmules adhere to the wall on account of the cage of spicules in which each of them is enclosed, but long before the water rises again the cages disintegrate and the gemmules are set free. Many of them fall or are carried by the wind into the water, on the surface of which, owing to their thick pneumatic coat, they float buoyantly. Others are lodged in cavities in the wall. On the water the force of gravity attracts them to one another and to the edge of the pond, and as the water rises they are carried against the wall and germinate. In thick jungle at the base of the Dawna Hills near Kawkareik[^[AI]] in the interior of Tenasserim, I found the leaves of shrubs which grew round a small pool, covered with little dry patches of the sponge, which had evidently grown upon them when the bushes were submerged. This was in March, during an unusually severe drought.

20. Trochospongilla pennsylvanica* (Potts).

Tubella pennsylvanica, Potts, P. Ac. Philad. 1882, p. 14. Tubella pennsylvanica, id., ibid. 1887, p. 251, pl. vi, fig. 2, pl. xii, figs. 1-3. Tubella pennsylvanica, Mackay, Trans. Roy. Soc. Canada, 1889, Sec. iv, p. 95. Tubella pennsylvanica, Hanitsch, Nature, li, p. 511 (1895). Tubella pennsylvanica, Weltner, Arch. Naturg. lxi (i), p. 128 (1895). Tubella pennsylvanica, Hanitsch, Irish Natural. iv, p. 129 (1895). Tubella pennsylvanica, Annandale, J. Linn. Soc., Zool., xxx, p. 248 (1908). Tubella pennsylvanica, id., Rec. Ind. Mus. iii, p. 102 (1909). Tubella pennsylvanica, id., P. U.S. Mus. xxxvii, p. 403, fig. 2 (1909).

Sponge soft, fragile, forming small cushion-shaped masses, grey or green; oscula few in number, often raised on sloping eminences surrounded by radiating furrows below the external membrane; external membrane adhering to the parenchyma.

Skeleton close, almost structureless. "Surface of mature specimens often found covered with parallel skeleton spicules, not yet arranged to form cell-like interspaces" (Potts).

Spicules. Skeleton-spicules slender, cylindrical, almost straight, sharp or blunt, minutely, uniformly or almost uniformly spined; spines sometimes absent at the tips. No flesh-spicules. Gemmule-spicules with the lower rotula invariably larger than the upper; both rotulæ flat or somewhat sinuous in profile, usually circular but sometimes asymmetrical or subquadrate in outline, varying considerably in size.

Gemmules small, numerous or altogether absent, covered with a granular pneumatic coat of variable thickness; the rotulæ of the gemmule-spicules overlapping and sometimes projecting out of the granular coat.

The measurements of the spicules and gemmules of an Indian specimen and of one from Lehigh Gap, Pennsylvania, are given for comparison:—

The spicules of the Travancore specimen are, therefore, a trifle larger than those of the American one, but the proportions are closely similar.

The difference between the gemmule-spicules of this species and those of such a form as T. phillottiana is merely one of degree and can hardly be regarded as a sufficient justification for placing the two species in different genera. If, as I have proposed, we confine the generic name Tubella to those species in which the gemmule-spicules are really like "little trumpets," the arrangement is a much more natural one, for these species have much in common apart from the gemmule-spicules. T. pennsylvanica does not appear to be very closely related to any other known species except T. phillottiana.

Type in the U.S. National Museum, from which specimens that appear to be co-types have been sent to the Indian Museum.

Geographical Distribution.—Very wide and apparently discontinuous:—N. America (widely distributed), Ireland (Hanitsch), Hebrides of Scotland (Annandale), Travancore, S. India (Annandale). The only Indian locality whence I have obtained specimens is Shasthancottah Lake near Quilon in Travancore.

Biology.—In Shasthancottah Lake T. pennsylvanica is found on the roots of water-plants that are matted together to form floating islands. It appears to avoid light and can only be obtained from roots that have been pulled out from under the islands. In Scotland I found it on the lower surface of stones near the edge of Loch Baa, Isle of Mull. In such circumstances the sponge is of a greyish colour, but specimens of the variety minima taken by Potts on rocks and boulders in Bear Lake, Pennsylvania, were of a bright green.

Sponges taken in Travancore in November were full of gemmules; in my Scottish specimens (taken in October) I can find no traces of these bodies, but embryos are numerous.

Genus 6. TUBELLA, Carter.

Tubella, Carter, Ann. Nat. Hist. (5) vii, p. 96 (1881). Tubella, Potts (partim), P. Ac. Philad. 1887, p. 248. Tubella, Weltner (partim), Arch. Naturg. lxi (i), p. 128 (1895).

Type, Spongilla paulula, Bowerbank.

This genus is distinguished from Ephydatia and Trochospongilla by the fact that the two ends of the gemmule-spicules are unlike not only in size but also in form. It sometimes happens that this unlikeness is not so marked in some spicules as in others, but in some if not in all the upper end of the shaft (that is to say the end furthest removed from the inner coat of the gemmule in the natural position) is reduced to a rounded knob, while the lower end expands into a flat transverse disk with a smooth or denticulated edge. The spicule thus resembles a little trumpet resting on its mouth. The shaft of the spicule is generally slender and of considerable length. The skeleton of the sponge is as a rule distinctly reticulate and often hard; the skeleton-spicules are either slender or stout and sometimes change considerably in proportions and outline as they approach the gemmules.

Geographical Distribution.—The genus is widely distributed in the tropics of both Hemispheres, its headquarters apparently being in S. America; but it is nowhere rich in species. Only two are known from the Oriental Region, namely T. vesparium* from Borneo, and T. vesparioides* from Burma.

21. Tubella vesparioides*, Annandale. ([Plate II], fig. 4.)

Tubella vesparioides, Annandale, Rec. Ind. Mus. ii, p. 157 (1908).

Sponge forming rather thick sheets of considerable size, hard but brittle, almost black in colour; oscula inconspicuous; external membrane supported on a reticulate horizontal skeleton.

Skeleton. The surface covered with a network of stout spicule-fibres, the interstices of which are more or less deeply sunk, with sharp fibres projecting vertically upwards at the nodes; the whole mass pervaded by a similar network, which is composed of a considerable number of spicules lying parallel to one another, overlapping at the ends and bound together by a profuse secretion of spongin.

Fig. 25.—Spicules of Tubella vesparioides (from type specimen). × 240.

Spicules. Skeleton-spicules slender, smooth, amphioxous, bent in a wide arc or, not infrequently, at an angle. No true flesh-spicules. Gemmule-spicules terminating above in a rounded, knob-like structure and below in a relatively broad, flat rotula, which is very deeply and irregularly indented round the edge when mature, the spicules at an earlier stage of development having the form of a sharp pin with a round head; shaft of adult spicules projecting slightly below the rotula, long, slender, generally armed with a few stout conical spines, which stand out at right angles to it.

Gemmules numerous throughout the sponge, spherical, provided with a short, straight foraminal tubule, surrounded by one row of spicules, which are embedded in a rather thin granular coat.

This sponge is closely related to Tubella vesparium (v. Martens) from Borneo, from which it may be distinguished by its smooth skeleton-spicules and the deeply indented disk of its gemmule-spicules. The skeleton-fibres are also rather less stout. By the kindness of Dr. Weltner, I have been able to compare types of the two species.

Type in the Indian Museum.

Habitat.—Taken at the edge of the Kanghyi ("great pond") at Mudon near Moulmein in the Amherst district of Tenasserim. The specimens were obtained in March in a dry state and had grown on logs and branches which had evidently been submerged earlier in the year. The name vesparium given to the allied species on account of its resemblance to a wasps' nest applies with almost equal force to this Burmese form.

Genus 7. CORVOSPONGILLA, nov.

Type[^[AJ]], Spongilla loricata, Weltner.

Spongillidæ in which the gemmule-spicules are without a trace of rotulæ and the flesh-spicules have slender cylindrical shafts that bear at or near either end a circle of strong recurved spines. The gemmule-spicules are usually stout and sausage-shaped, and the gemmules resemble those of Stratospongilla in structure. The skeleton is strong and the skeleton-spicules stout, both resembling those of the "genus" Potamolepis, Marshall.

As in all other genera of Spongillidæ the structure of the skeleton is somewhat variable, the spicule-fibres of which it is composed being much more distinct in some species than in others. The skeleton-spicules are often very numerous and in some cases the skeleton is so compact and rigid that the sponge may be described as stony. The flesh-spicules closely resemble the gemmule-spicules of some species of Ephydatia and Heteromeyenia.

Geographical Distribution.—The species of this genus are probably confined to Africa (whence at least four are known) and the Oriental Region. One has been recorded from Burma and another from the Bombay Presidency.

Key to the Indian Species of Corvospongilla.

22. Corvospongilla burmanica* (Kirkpatrick). ([Plate II], fig. 5.)

Spongilla loricata var. burmanica, Kirkpatrick, Rec. Ind. Mus. ii, p. 97, pl. ix (1908).

Sponge forming a shallow sheet, hard, not very strong, of a pale brownish colour; the surface irregularly spiny; the oscula small but conspicuous, circular, raised on little turret-like eminences; the external membrane adhering closely to the sponge.

Skeleton dense but by no means regular; the network composed largely of single spines; thick radiating fibres distinguishable in the upper part of the sponge.

Spicules. Skeleton-spicules smooth, not very stout, amphistrongylous, occasionally a little swollen at the ends, often with one or more fusiform swellings, measuring on an average about 0.27 × 0.0195 mm. Flesh-spicules with distinct rotules, the recurved spines numbering 4 to 6, measuring about 1/7 the length of the spicules; the shaft by no means strongly curved; their length from 0.03-0.045 mm. Gemmule-spicules amphioxous, as a rule distinctly curved, sometimes swollen at the ends, covered regularly but somewhat sparsely with fine spines, not measuring more than 0.49 × 0.078 mm.

Gemmules strongly adherent, arranged in small groups, either single or double; when single spherical, when double oval; each gemmule or pair of gemmules covered by two layers of gemmule-spicules bound together in chitinous substance; the inner layer on the inner coat of the gemmule, the outer one separated from it by a space and in contact with the outer cage of skeleton-spicules; the size of the gemmule-spicules variable in both layers; external to the outer layer a dense cage of skeleton-spicules; foraminal tubule short, cylindrical.

This sponge is closely related to S. loricata, Weltner, of which Kirkpatrick regards it as a variety. "The main difference," he writes, "between the typical African form and the Burmese variety consists in the former having much larger microstrongyles (83 × 15.7 µ [0.83 × 0.157 mm.]) with larger and coarser spines;... Judging from Prof. Weltner's sections of gemmules, these bodies lack the definite outer shell of smooth macrostrongyles [blunt skeleton-spicules], though this may not improbably be due to the breaking down and removal of this layer. A further difference consists in the presence, in the African specimen, of slender, finely spined strongyles [amphistrongyli], these being absent in the Burmese form, though perhaps this fact is not of much importance."

Type in the British Museum; a piece in the Indian Museum.

Habitat.—Myitkyo, head of the Pegu-Sittang canal, Lower Burma (E. W. Oates).

Biology.—The sponge had grown over a sheet of the polyzoon Hislopia lacustris, Carter (see p. 204), remains of which can be detected on its lower surface.

"Mr. E. W. Oates, who collected and presented the sponge, writes that the specimen was found encrusting the vertical and horizontal surfaces of the bottom beam of a lock gate, where it covered an area of six square feet. The beam had been tarred several times before the sponge was discovered. The portion of the gate on which the sponge was growing was submerged from November to May for eight hours a day at spring tides, but was entirely dry during the six days of neap tides. From May to October it was constantly submerged. The sponge was found in April. Although the canal is subject to the tides, the water at the lock is always fresh. The colour of the sponge during life was the same as in its present condition."

23. Corvospongilla lapidosa* (Annandale).

Spongilla lapidosa Annandale, Rec. Ind. Mus. ii, pp. 25, 26, figs. 3, 4, 5 (1908).

The sponge forms a thin but extremely hard and resistant crust the surface of which is either level, slightly concave, or distinctly corrugated; occasional groups of spicules project from it, but their arrangement is neither so regular nor so close as is the case in C. burmanica. The dermal membrane adheres closely to the sponge. The oscula are small; some of them are raised above the general surface but not on regular turret-shaped eminences. The colour is grey or black. There is a thick chitinous membrane at the base of the sponge.

Fig. 26.—Spicules of Corvospongilla lapidosa (from type specimen), × 240.

The skeleton is extremely dense owing to the large number of spicules it contains, but almost structureless; broad vertical groups of spicules occur but lack spongin and only traverse a small part of the thickness of the sponge; their position is irregular. The firmness of the skeleton is due almost entirely to the interlocking of individual spicules. At the base of the sponge the direction of a large proportion of the spicules is horizontal or nearly horizontal, the number arranged vertically being much greater in the upper part.

Spicules. The skeleton-spicules are sausage-shaped and often a little swollen at the ends or constricted in the middle. A large proportion are twisted or bent in various ways, and a few bear irregular projections or swellings. The majority, however, are quite smooth. Among them a few more or less slender, smooth amphioxi occur, but these are probably immature spicules. The length and curvature of the amphistrongyli varies considerably, but the average measurements are about 0.28 × 0.024 mm. The flesh-spicules also vary greatly in length and in the degree to which their shafts are curved. At first sight it seems to be possible to separate them into two categories, one in which the shaft is about 0.159 mm. long, and another in which it is only 0.05 mm. or even less; and groups of birotulates of approximately the same length often occur in the interstices of the skeleton. Spicules of all intermediate lengths can, however, be found. The average diameter of the shaft is 0.0026 mm. and of the rotula 0.0106 mm., and the rotula consists of from 6 to 8 spines. The gemmule-spicules vary greatly in size, the longest measuring about 0.08 × 0.014 and the smallest about 0.034 × 0.007 or even less. There appears to be in their case an even more distinct separation as regards size than there is in that of the flesh-spicules; but here again intermediate forms occur. They are all stout, more or less blunt, and more or less regularly covered with very short spines; most of them are distinctly curved, but some are quite straight.

Gemmules. The gemmules are firmly adherent to the support of the sponge, at the base of which they are congregated in groups of four or more. They vary considerably in size and shape, many of them being asymmetrical and some elongate and sausage-shaped. The latter consist of single gemmules and not of a pair in one case. Extreme forms measure 0.38 × 0.29 and 0.55 × 0.25. Each gemmule is covered with a thick chitinous membrane in close contact with its wall and surrounding it completely. This membrane is full of spicules arranged as in a mosaic; most or all of them belong to the smaller type, and as a rule they are fairly uniform in size. Separated from this layer by a considerable interval is another layer of spicules embedded in a chitinous membrane which is in continuity with the basal membrane of the sponge. The spicules in this membrane mostly belong to the larger type and are very variable in size; mingled with them are often a certain number of birotulate flesh-spicules. The membrane is in close contact with a dense cage of skeleton-spicules arranged parallel to it and bound together by chitinous substance. The walls of this cage, when they are in contact with those of the cages of other gemmules, are coterminous with them. There is a single depressed aperture in the gemmules, as a rule situated on one of the longer sides.

This sponge is distinguished from C. burmanica not only by differences in external form, in the proportions of the spicules and the structure of the skeleton, but also by the peculiar nature of the armature of the gemmule. The fact that birotulate spicules are often found in close association with them, is particularly noteworthy.

Type in the Indian Museum.

Geographical Distribution.—This sponge has only been found in the Western Ghats of the Bombay Presidency. Localities:—Igatpuri Lake and the R. Godaveri at Nasik.

Biology.—There is a remarkable difference in external form between the specimens taken in Igatpuri and those from Nasik, and this difference is apparently due directly to environment. In the lake, the waters of which are free from mud, the sponges were growing on the lower surface of stones near the edge. They formed small crusts not more than about 5 cm. (2 inches) in diameter and of a pale greyish colour. Their surface was flat or undulated gently, except round the oscula where it was raised into sharply conical eminences with furrowed sides. The specimens from Nasik, which is about 30 miles from Igatpuri, were attached, together with specimens of Spongilla cinerea and S. indica, to the sides of a stone conduit full of very muddy running water. They were black in colour, formed broad sheets and were markedly corrugated on the surface. Their oscula were not raised on conical eminences and were altogether most inconspicuous. The skeleton was also harder than that of sponges from the lake.

In the lake C. lapidosa was accompanied by the gemmules of Spongilla bombayensis, but it is interesting that whereas the latter sponge was entirely in a resting condition, the former was in full vegetative vigour, a fact which proves, if proof were necessary, that the similar conditions of environment do not invariably have the same effect on different species of Spongillidæ.

[W] O. von Linstow, Rec. Ind. Mus. i, p. 45 (1907).

[X] W. M. Tattersall, ibid., ii, p. 236 (1908).

[Y] T. R. R. Stebbing, ibid., i, p. 160 (1907); and N. Annandale, ibid., ii, p. 107 (1908).

[Z] Mr. Stebbing has been kind enough to examine specimens of this isopod, which he will shortly describe in the Records of the Indian Museum. S. walkeri, its nearest ally, was originally described from the Gulf of Manaar, where it was taken in a tow-net gathering (see Stebbing in Herdman's Report on the Ceylon Pearl Fisheries, pt. iv, p. 31 (1905)).

[AA] See M. and A. Weber in M. Weber's Zool. Ergeb. Niederl. Ost-Ind. vol. i, p. 48, pl. v (1890).

[AB] Mr. C. A. Paiva, Assistant in the Indian Museum, has lately (March 31st, 1911) obtained specimens of S. crateriformis in a small pond of fresh water on Ross Island in the Andaman group. The existence of this widely distributed species on an oceanic island is noteworthy.

[AC] The only complete European specimen of the species I have seen differs considerably in outward form from any Indian variety, consisting of a flat basal area from which short, cylindrical turret-like branches arise. This specimen is from Lake Balaton in Hungary and was sent me by Prof. von Daday de Dees of Buda-Pesth.

[AD] Needham. Rec. Ind. Mus. iii, p. 206 (1909).

[AE] According to the late Rai Bahadur R. B. Sanyal, freshwater sponges are called in Bengali "shrimps' nests." From his description it is evident that he refers mainly to S. carteri (see Hours with Nature, p. 46; Calcutta 1896).

[AF] Stebbing, J. Linn. Soc. xxx, p. 40; Annandale, Rec. Ind. Mus. i, p. 279.

[AG] Brunetti, Rec. Ind. Mus. ii, p. 376 (1908).

[AH] The outer covering by means of which the gemmule is fixed is not formed until the other structures are complete. In young sponges, therefore, free gemmules may often be found.

[AI] This locality is often referred to in zoological literature as Kawkareet or Kawkarit, or even Kokarit.

[AJ] Potts's Spongilla novæ-terræ from Newfoundland and N. America cannot belong to this genus although it has similar flesh-spicules, for, as Weltner has pointed out (op. cit. supra p. 126), the gemmule-spicules are abortive rotulæ. This is shown very clearly in the figure published by Petr (Rozp. Ceske Ak. Praze, Trída, ii, pl. ii, figs. 27, 28, 1899), who assigns the species to Heteromeyenia. Weltner places it in Ephydatia, and it seems to be a connecting link between the two genera. It has been suggested that it is a hybrid (Traxler, Termes. Fuzetek, xxi, p. 314, 1898).

APPENDIX TO PART I.

Form of Uncertain Position.

([Plate I], fig. 4.)

On more than one occasion I have found in my aquarium in Calcutta small sponges of a peculiar type which I am unable to refer with certainty to any of the species described above. Fig. 4, pl. I, represents one of these sponges. They are never more than about a quarter of an inch in diameter and never possess more than one osculum. They are cushion-shaped, colourless and soft. The skeleton-spicules are smooth, sharply pointed, moderately slender and relatively large. They are arranged in definite vertical groups, which project through the dermal membrane, and in irregular transverse formation. Small spherical gemmules are present but have only a thin chitinous covering without spicules or foramen.

These sponges probably represent an abnormal form of some well-known species, possibly of Spongilla carteri. I have seen nothing like them in natural conditions.

PART II.
FRESHWATER POLYPS
(HYDRIDA).

INTRODUCTION TO PART II.

I.

The Phylum Cœlenterata and the Class Hydrozoa.

The second of the great groups or phyla into which the metazoa are divided is the Cœlenterata, in which are included most of the animals commonly known as zoophytes, and also the corals, sea-anemones and jelly-fish. These animals are distinguished from the sponges on the one hand and from the worms, molluscs, arthropods, vertebrates, etc., on the other by possessing a central cavity (the cœlenteron or "hollow inside") the walls of which are the walls of the body and consist of two layers of cells separated by a structureless, or apparently structureless, jelly. This cavity has as a main function that of a digestive cavity.

An ideally simple cœlenterate would not differ much in general appearance from an olynthus (p. 27), but it would have no pores in the body-wall and its upper orifice would probably be surrounded by prolongations of the body-wall in the form of tentacles. There would be no collar-cells, and the cells of the body generally would have a much more fixed and definite position and more regular functions than those of any sponge. The most characteristic of them would be the so-called cnidoblasts. Each of these cells contains a capsule[^[AK]] from which a long thread-like body can be suddenly uncoiled and shot out.

The simplest in structure of the cœlenterates are those that constitute the class Hydrozoa. In this class the primitive central cavity is not divided up by muscular partitions and there is no folding in of the anterior part of the body to form an œsophagus or stomatodæum such as is found in the sea-anemones and coral polyps. In many species and genera the life-history is complex, illustrating what is called the alternation of generations. That is to say, only alternate generations attain sexual maturity, those that do so being produced as buds from a sexless generation, which itself arises from the fertilized eggs of a previous sexual generation. The sexual forms as a rule differ considerably in structure from the sexless ones; many medusæ are the sexual individuals in a life-cycle in which those of the sexless generation are sedentary.