THE INTERNATIONAL SCIENTIFIC SERIES.

VOLUME XIX.

THE INTERNATIONAL SCIENTIFIC SERIES.

Works already Published.

THE INTERNATIONAL SCIENTIFIC SERIES.

ANIMAL PARASITES AND MESSMATES.

BY

P. J. VAN BENEDEN,

PROFESSOR AT THE UNIVERSITY OF LOUVAIN,
CORRESPONDENT OF THE INSTITUTE OF FRANCE.

WITH EIGHTY-THREE ILLUSTRATIONS.

NEW YORK:

D. APPLETON AND COMPANY,

549 & 551 BROADWAY.
1876.

INTRODUCTION.

“The edifice of the world is only sustained by the impulses of hunger and love.”—Schiller.

In that great drama which we call Nature, each animal plays its especial part, and He who has adjusted and regulated everything in its due order and proportion, watches with as much care over the preservation of the most repulsive insect, as over the young brood of the most brilliant bird. Each, as it comes into the world, thoroughly knows its part, and plays it the better because it is more free to obey the dictates of its instinct. There presides over this great drama of life a law as harmonious as that which regulates the movements of the heavenly bodies; and if death carries off from the scene every hour myriads of living creatures, each hour life causes new legions to rise up in order to replace them. It is a whirlwind of being, a chain without end.

This is now more fully known; whatever the animal may be, whether that which occupies the highest or the lowest place in the scale of creation, it consumes water and carbon, and albumen sustains its vital force.

Therefore, the Hand which has brought the world out of chaos, has varied the nature of this food; it has proportioned this universal nourishment to the necessities and the peculiar organization of the various species which have to derive from it the power of motion and the continuance of their lives.

The study whose aim is to make us acquainted with the kind of food adapted to each animal constitutes an interesting branch of Natural History. The bill of fare of every animal is written beforehand in indelible characters on each specific type; and these characters are less difficult for the naturalist to decipher than are palimpsests for the archæologist.

Under the form of bones or scales, of feathers or shells, they show themselves in the digestive organs. It is by paying, not domiciliary, but stomachic visits, that we must be initiated into the details of this domestic economy. The bill of fare of fossil animals, though written in characters less distinct and complete, can still be very frequently read in the substance of their coprolites. We do not despair even to find some day the fishes and the crustaceans which were chased by the plesiosaurs and the ichthyosaurs, and to discover some parasitic worms which had entered with them into the convolutions of the intestines of the saurians.

Naturalists have not always studied with sufficient care the correspondence which exists between the animal and its food, although it supplies the student with information of a very valuable kind. In fact, every organized body, whether conferva or moss, insect or mammal, becomes the prey of some animal; every organic substance, sap or blood, horn or feather, flesh or bone, disappears under the teeth

of some one or other of these; and to each kind of débris correspond the instruments suitable for its assimilation. These primary relations between living beings and their alimentary regimen call forth the activity of every species.

We find, on closer examination, more than one analogy between the animal world and human society; and without much careful scrutiny, we may say that there is no social position which has not (if I may dare to use the expression) its counterpart among the lower animals.

The greater part of these live peaceably on the fruit of their labour, and carry on a trade by which they gain their livelihood; but by the side of these honest workers we find also some miserable wretches who cannot do without the assistance of their neighbours, and who establish themselves, some as parasites in their organs, others as uninvited guests, by the side of the booty which they have gained.

Some years ago, one of our learned and ingenious colleagues at the University of Utrecht, Professor Harting, wrote a charming book on the industry of animals, and demonstrated that almost every trade is known in the animal kingdom. We find among them miners, masons, carpenters, paper manufacturers, weavers, and we may even say lace-makers, all of whom work first for themselves, and afterwards for their progeny. Some dig the earth, construct and support vaults, clear away useless earth, and consolidate their works, like miners; others build huts or palaces according to all the rules of architecture; others know intuitively all the secrets of the manufacturers of paper, cardboard, woollen stuffs or lace; and their productions need not fear comparison with

the point-lace of Mechlin or of Brussels. Who has not admired the ingenious construction of the beehive or of the ant-hill, or the delicate and marvellous structure of the spider’s web? The perfection of some of these works is so great and so generally appreciated, that when the astronomer requires for his telescope a slender and delicate thread, he applies to a living shop, to a simple spider. When the naturalist wishes to test the comparative excellence of his microscope, or requires a micrometer for infinitely little objects, he consults, not a millimetre, divided and subdivided into a hundred or a thousand parts, but the simple carapace of a diatom, so small and indistinct that it is necessary to place a hundred of them side by side to render them visible to the naked eye: and still more, the best microscopes do not always reveal all the delicacy of the designs which decorate these Lilliputian frustules. Mons. H. Ph. Adan has lately shown, with an artist’s talent, the infinite beauties which the microscope reveals in this invisible world.

To whom do the manufacturers of Verviers or of Lyons, of Ghent or of Manchester, apply for their raw materials? Either to an animal or a plant; and even up to the present time we have had sufficient modesty not to have sought to imitate either wool or cotton. Yet these animal manufacturers carry on their operations every day under our eyes, the doors wide open to everybody, and none of them is as yet marked with the trite expression, “No admittance.”

“The beau-ideal which we place before us in the arts of spinning and weaving,” said an inhabitant of the South to Michelet, “is the beautiful

hair of a woman: the softest wool, the finest cotton, is very far from realizing it.” The Southerner seemed to forget that this soft wool, as well as this fine cotton, was not the product of our manufacturers any more than the woman’s hair.

Were these animal machines to sustain injury, or even to be idle for a certain time, we should be reduced to have nothing wherewith to cover our shoulders: the fine lady would have neither Cashmere shawl, silk, nor velvet in her wardrobe; we should have neither flannel nor cloth to make our clothes; the herdsman even would not have his goat’s skin to protect him from the inclemency of the season. Thanks to the animal which gives us his flesh and his fleece, we are able to leave the southern regions, to brave the rigour of other climes, and establish ourselves side by side with the reindeer and the narwhal, in the midst of eternal snow.

We have our science and our steam-engines, of which we are justly proud; the animals have only their simple instinct to enable them to fabricate their marvellous tissues, and yet they succeed better than ourselves. The so-called blind forces of nature produce thread, the use of which the genius of man seeks in vain to supersede; and we do not even dream of entering into competition with these living machines which we daily crush under our feet.

All these occupations are openly carried on; and if there are some which are honest, it may be said that there are others which deserve another character. In the ancient as well as the new world, more than one animal resembles somewhat the sharper leading the life of a great

nobleman; and it is not rare to find, by the side of the humble pickpocket, the audacious brigand of the high road, who lives solely on blood and carnage. A great proportion of these creatures always escape, either by cunning, by audacity, or by superior villainy, from social retribution.

But side by side with these independent existences, there are a certain number which, without being parasites, cannot live without assistance, and which demand from their neighbours, sometimes only a resting-place in order to fish by their side, sometimes a place at their table, that they may partake with them of their daily food; we find some every day which used to be considered parasites, yet which by no means live at the expense of their hosts.

When a copepod crustacean instals himself in the pantry of an ascidian, and filches from him some dainty morsel, as it passes by; when a benevolent animal renders some service to his neighbour, either by keeping his back clean, or removing detritus which clogs certain organs, this crustacean or this animal is no more a parasite than is he who cowers by the side of a vigilant and skilful neighbour, quietly takes his siesta, and is contented with the fragments which fall from the jaws of his companion. We may say the same thing of the fish which, through idleness, attaches itself, like the remora, to a neighbour who swims well, and fishes by his side without fatiguing his own fins.

The services of many of these are rewarded either in protection or in kind, and mutuality can well be exercised at the same time as hospitality.

Those creatures which merit the name of parasites feed at the expense

of a neighbour, either establishing themselves voluntarily in his organs, or quitting him after each meal, like the leech or the flea.

But when the larva of an ichneumon devours, organ after organ, the caterpillar which serves him as a nurse, and at last eats her entirely, can we call him a parasite? According to Lepelletier de Saint-Fargeau, who has so successfully treated these questions, the parasite is he who lives at the expense of another, eating that which belongs to him, but not devouring his nurse herself. Nor is the ichneumon a carnivorous animal, for the true beast of prey cares nothing at any period of his existence for the life of his victim.

True parasites are very commonly found in nature, and we should be wrong were we to consider that they all live a sad and monotonous life. Some among them are so active and vigilant that they sustain themselves during the greater part of their life, and only seek for assistance at certain determinate periods. They are not, as has been supposed, exceptional and strange beings, without any other organs than those of self-preservation. There is not, as was formerly supposed, a class of parasites, but all the classes of the animal kingdom include some among their inferior ranks.

We may divide them into different categories.

In the first of these we will place together all those which are free at the commencement of their life, which swim and take their sport without seeking assistance from others, until the infirmities of age compel them to retire into a place of refuge. They live at first like true Bohemians, and are certain of getting invalided at last in some well-arranged asylum. Sometimes both the male and female require this

assistance at a certain age; with others it is the female only, as the male continues his wandering life. In some cases, the female carries her partner with her, and supports him entirely during his captivity; her host nourishes her, and she in her turn feeds her husband. We find few female gill-suckers which have not with them their Lilliputian males, which, like a shadow, never quit them. But we also find males, living as parasites of their females, among those curious crustaceans known by the name of cirrhipeds. All the parasitical crustaceans are placed in this first category.

We find others, the ichneumons for example, which are perfectly at liberty in their old age, but require protection while young. There are many of these, which as soon as they escape from the egg, are literally put out to nurse; but from the day when they cast off their larval robe, they are no longer under restraint, but, armed cap-à-pie, they rush eagerly in quest of adventure, and die like others on the high road. In this category are generally found parasitical hymenopterous and dipterous insects.

Other kinds are lodgers all their lives, though they change their hosts, not to say their establishment, accordingly to their age and constitution. As soon as they quit the egg, they seek for the favours of others, and all their itinerary is rigorously traced out for them beforehand. Fortunately we are at present acquainted with the halting-places and magazines of a great number of those which belong to the order of cestode and trematode worms. These flat and soft worms begin life usually as vagabonds, aided by a ciliary robe which serves

as an apparatus for locomotion; but scarcely have they tried to use their delicate oars, before they demand assistance, lodge themselves in the body of the first host that they meet, whom they abandon for another living lair, and then condemn themselves to perpetual seclusion.

That which adds to the interest inspired by these feeble and timid beings is, that at each change of abode, they change also their costume; and that when they have reached the limit of their peregrinations, they assume the virile toga—we had almost said, the wedding robe. The sexes appear only under this later envelope; up to this period they have had no thoughts of the cares of a family. It has always been somewhat difficult to establish the identity of those persons who frequent the public saloons one day, and are found on the next in the most obscure haunts, dressed as mendicants. Most of the worms which have the form of a leaf or a tape give themselves up to these peregrinations, and those which do not arrive at their last stage, die usually without posterity.

It is interesting to remark that these parasitical worms do not inhabit the various organs of their neighbours indiscriminately, but all begin their life modestly in an almost inaccessible attic, and end it in large and spacious apartments. At their first appearance they think only of themselves, and are contented to lodge, as scolices or vesicular worms, in the connective tissue of the muscles, of the heart, of the lobes of the brain, or even in the ball of the eye; at a later stage, they think of the cares of a family, and occupy large vessels like the digestive or respiratory passages, always

in free communication with the exterior; they have a horror of being enclosed, and the propagation of their species requires access to the outer air.

In the last category are found those which need assistance all their lives; as soon as they have penetrated into the body of their host, they never remove again, and the lodging which they have chosen serves them both as a cradle and a tomb.

Some years since, no one suspected that a parasite could live in any other animal than that in which it was discovered. All helminthologists, with few exceptions, looked upon worms in the interior of the body as formed without parents in the same organs which they occupy. Worms which are parasites of fish, had been seen a long time before this in the intestines of various birds: experiments had even been made to satisfy observers of the possibility of these creatures passing from one body to another; but all these experiments had only given a negative result, and the idea of inevitable transmigration was so completely unknown that Bremser, the first helminthologist of his age, raised the cry of heresy, when Rudolphi spoke of the ligulæ of fishes which could continue to live in birds.

At a period nearer to our own times, our learned friend, Von Siebold, deservedly called the prince of helminthologists, was entirely of this opinion, and compared the cysticercus of the mouse with the tape-worm of the cat, considering this young worm as a wandering, sick, and dropsical being.

In his opinion, the worm had lost its way in the mouse, as the tænia of the cat could live only in the cat. Flourens considered it a romance when I myself announced to the “Institut de France,” that

cestode worms must necessarily pass from one animal to another in order to complete the phases of their evolution.

At the present time, experiments respecting these transmigrations are repeated every day in the laboratories of zoology with the same success; and Mons. R. Leuckart, who directs with so much talent the Institute of Leipzig, has discovered, in concert with his pupil Mecznikow, transmigrations of worms accompanied by changes of sex; that is to say, they have seen nematodes, the parasites of the lungs of the frog, always female or hermaphrodite, produce individuals of the two sexes which do not resemble their mother, and whose habitual abode is not in the lungs of the frog but in damp earth. In other words, let us imagine a mother, born a widow, who cannot exist without the assistance of others, producing boys and girls able to provide for themselves. The mother is parasitical and viviparous, her daughters are, during their whole life, free and oviparous.

This observation leads us to another sexual singularity, lately observed, of males and females of different kinds in one and the same species, and which give birth to progeny which do not resemble each other; the same animals, or rather the same species, proceed from two different eggs fecundated by different spermatozoids.

Now that these transmigrations are perfectly known and admitted, the starting-point of the inquiry has been so entirely forgotten that the honour of the discovery has been frequently attributed to fellow-workers, who had no knowledge of it till the demonstration had been completed, and the new interpretation generally accepted. But let us return to our subject.

The assistance rendered by animals to each other is as varied as that which is found amongst men. Some receive merely an abode, others nourishment, others again food and shelter; we find a perfect system of board and lodging combined with philozoic institutions arranged in the most perfect manner. But if we see by the side of these paupers, some which render to one another mutual services, it would be but little flattering to them to call all indiscriminately either parasites or messmates (commensaux). We think that we should be more just to them if we designated the latter kinds mutualists, and thus mutuality will take its place by the side of mess-table arrangements (commensalism) and of parasitism.

It would also be necessary to coin another name for those which, like certain crustaceans, or even some birds, are rather guests which smell out a feast from afar (pique-assiettes) than parasites; and for others which repay by an ill turn the assistance which they have received. And what name shall we give to those which, like the plover, render services which may be compared to medical attendance?

This bird in fact performs the office of dentist to the crocodile. A small species of toad acts as an accoucheur to his female companion, making use of his fingers as a forceps to bring the eggs into the world. Again, the pique-bœuf performs a surgical operation, each time that he opens with his lancet the tumour which encloses a larva in the midst of the buffalo’s back. Nearer home, we see the starling render in our own meadows the same service as the pique-bœuf (Buphaga) in Africa; and we may see that among these living creatures there is more than one speciality in the healing art.

We must not forget that the occupation of a gravedigger is equally general in nature, and that it is never without some profit to himself or his progeny that this gloomy workman inters the bodies of the dead. Certain animals have an occupation analogous to that of the shoeblack or the scourer, and they freshen up with care, and even with a kind of coquettish pleasure, the toilet of their neighbours.

And how must we designate the birds known by the name of stercorariæ, which take advantage of the cowardice of sea-gulls in order to live in idleness? It is useless for the gulls to trust to the strength of their wings, the stercorariæ in the end compel them to disgorge their food in order that they may partake of the spoils of their fishery. When followed up too closely, these timid birds throw up the contents of their crop, to render themselves lighter, like the smuggler who finds no means of safety except in abandoning his load.

We must not, however, be too hard upon all this class, since very often, as in the case of the gnat, it is only one of the sexes which seeks a victim.

All animals usually live for the passing day; and yet there are some which practise economy, which are not ignorant of the advantages of the savings bank, and, like the raven and the magpie, think of the morrow, to lay up in store the superfluity of the day’s provision.

As we have before said, this little world is not always easy to be known, and in its societies, to which each brings his capital, some in activity, others in violence or in stratagem, we find more than one Robert Macaire who contributes nothing, and takes advantage of all. Every species of animal may have its parasites and its messmates,

and each may perhaps have some of different sorts, and in diverse categories.

But whence come those disgusting beings, whose name alone inspires us with horror, and which instal themselves without ceremony, not in our dwellings, but in our organs, and which we find it more difficult to expel than rats or mice? They all derive their existence from their parents.

The time has passed when a vitiated condition of the humours, or the deterioration of the parenchyma was considered a sufficient cause for the formation of parasites, and when their presence was regarded as an extraordinary phenomenon resulting from the morbid dispositions of the organism. We have reason to hope that this language will, during the next generation, have entirely disappeared from works on physiology and pathology. Neither the temperament nor the humours have any influence on parasites, and they are not more abundant in delicate individuals than in those who enjoy the most robust health. On the contrary, all wild animals harbour their parasitical worms, and the greater part of them have not lived long in captivity, before nematode and cestode worms completely disappear. It is only the imprisoned parasites which do not desert them.

All these mutual adaptations are pre-arranged, and as far as we are concerned, we cannot divest ourselves of the idea that the earth has been prepared successively for plants, animals, and man. When God first elaborated matter, He had evidently that being in view who was intended at some future day to raise his thoughts to Him, and do Him homage.

This is the answer which I would give to the question recently propounded by Mons. L. Agassiz. “Were the physical changes to which our globe has been subjected effected for the sake of the animal world, considered in its relations from the very beginning, or are the modifications of animals the result of physical changes?” in other words, has the earth been made and prepared for living beings, or have living beings been as highly developed as was possible, according to the physical vicissitudes of the planet which they inhabit?

This question has always been discussed, and that science which cannot look beyond its scalpel, will never succeed in resolving it. Each one must seek by his own reason the solution of the great problem.

When we see the newly-born colt eagerly seeking for its mother’s teats, the chick as soon as it is hatched beginning to peck, or the duckling seeking its puddle of water, can we recognize anything but instinct as the cause of these actions, and is not this instinct the libretto written by Him who has forgotten nothing?

The statuary who tempers the clay from which to make his model, has already conceived in his mind the statue which he is about to produce. Thus it is with the Supreme Artist. His plan for all eternity is present to His thought. He will execute the work in one day, or in a thousand ages. Time is nothing to Him; the work is conceived, it is created, and each of its parts is only the realization of the creative thought, and its predetermined development in time and space.

“The more we advance in the study of nature,” says Oswald Heer in “Le Monde primitif” which he has just published, “the more profound also is our conviction, that belief in an Almighty Creator and a Divine

Wisdom, who has created the heavens and the earth according to an eternal and preconceived plan, can alone resolve the enigmas of nature, as well as those of human life. Let us still erect statues to men who have been useful to their fellow-creatures, and have distinguished themselves by their genius, but let us not forget what we owe to Him who has placed marvels in each grain of sand, a world in every drop of water.”

At first we shall treat of animal messmates, secondly of mutualists, and thirdly of parasites.

ANIMAL PARASITES

AND MESSMATES.

CHAPTER I.

ANIMAL MESSMATES.

The messmate is he who is received at the table of his neighbour to partake with him of the produce of his day’s fishing; it would be necessary to coin a name to designate him who only requires from his neighbour a simple place on board his vessel, and does not ask to partake of his provisions.

The messmate does not live at the expense of his host; all that he desires is a home or his friend’s superfluities. The parasite instals himself either temporarily or definitively in the house of his neighbour; either with his consent or by force, he demands from him his living, and very often his lodging.

But the precise limit at which commensalism begins is not always easily to be ascertained. There are animals which live as messmates with others only at a certain period of their lives, and which provide for their own support at other times; others are only messmates under

certain given circumstances, and do not usually merit this appellation.

In the higher animals, this relation between them is generally well known, and justly appreciated, but it is not the same in the inferior ranks; and more than one animal may pass for a messmate or a parasite, for a robber or for a mendicant, according to the circumstances under which he is observed. The sharper passes for an honest man as long as he has not been taken in flagrante delicto. Thus, in order to be just, we must carefully examine the indictment, and not pronounce sentence without strict examination.

The greater part of those animals which have established themselves on each other, and live together on a good understanding and without injury, are wrongly classed as parasites by the generality of naturalists. Now that the mutual relations of many of these are better understood, we know many animals which unite together to render each other mutual assistance; while there are others which live like paupers on the crumbs which fall from the rich man’s table. There are many relations between the different species which can be discovered only after minute examination, but which have recently been appreciated with greater impartiality.

Animal messmates are rather numerous, and commensalism has been observed, not only in animals of the present age, but in those of the primary epoch. Wyville Thomson explained to me, while I was myself his messmate at Edinburgh, at the meeting of the British Association in 1871, that the polyps of the Silurian age already practised it. We do not class among animal messmates those living creatures which, like the birds which we keep in cages, charm the ear with their song, or

which, in spite of our care, live at the expense of our pantry; we will only refer to veritable messmates, which, sometimes through weakness of constitution, sometimes for want of activity, can neither feed themselves nor bring up their family without seeking help from their neighbours.

There are some free messmates which never renounce their independence, whatever may be the advantages which their Amphitryon enjoys; they break their alliance with him for the slightest motive of discontent, and go and seek their fortune elsewhere. Their susceptibility or their love of change guides them. They are recognized by their fishing implements or their travelling gear, which they never lay aside. These free messmates are the more numerous. The others, the fixed messmates, instal themselves with a neighbour, and live at their ease, having completely changed their dress, and renounced for ever an independent life. Their fate is thenceforward bound to him who carries them.

Under these two categories we shall cite several examples, and glance at the differences which the various classes of the animal kingdom present in this respect, beginning with the higher ranks.

CHAPTER II.

FREE MESSMATES.

We meet with free messmates in various classes of the animal kingdom. They sometimes mount on the back of a neighbour, sometimes occupy the opening of the mouth, the digestive passages, or the exit for the excreta; at times they place themselves under the shelter of the cloak of their host, from whom they receive both aid and protection.

Among the vertebrates, there are few except fishes which merit a place here; it is only amongst these that we meet with species at the mercy of others, and dependent on acolytes, which are in every respect inferior to themselves.

An interesting messmate belonging to this first category is a fish of graceful form, named donzelina, which goes to seek its fortune in the body of a holothuria. Naturalists have long known it under the name of Fierasfer. It has a long body like that of an eel, entirely covered with small scales; and as it is quite compressed, it has been compared to the sword which conjurors thrust into their œsophagus. They are found in different seas, and all have similar habits. This fish is lodged in the digestive tube of his companion, and,

without any regard for the hospitality which he receives, he seizes on his portion of all that enters. The Fierasfer contrives to cause himself to be served by a neighbour better provided than himself with the means of fishing.

Dr. Greef, at present Professor at Marbourg, found at Madeira a holothuria of a foot in length, in which a vigorous Fierasfer lived in peace. Quoy and Gaimard, in the account of their voyage round the world, have remarked long since, that the Fierasfer hornei is found in the Stichopus tuberculosus.

The holothuriæ seem to exist under very advantageous conditions in this respect, since we see Fierasfers, which are themselves tolerable gluttons, accompanied by Palæmons and Pinnotheres in the same animal. Professor C. Semper has seen holothuriæ in the Philippine Islands which bore a considerable resemblance, in this respect, to an hotel with its table d’hôte.

These singular fishes have been long noticed, but it was not till recently that their presence in a host so low in the scale as a holothurian could be explained.

But if naturalists are agreed as to the bond which unites these fishes to the holothuriæ, they do not agree as to the organs which they inhabit in their living hotel. Do they lodge in the digestive cavity of the holothuriæ, or do they inhabit the arborescent respiratory processes which open at the posterior extremity of the body? Until recently it was thought that it was in their stomach, but a doubt has arisen. Professor Semper, who has studied these animals with particular care at the Philippine Islands, had the curiosity to open

the stomach of some of them, and found there, not the animals taken by the holothuriæ, but the remains of its respiratory processess which they were in the act of digesting. Is it then merely a messmate? We must have more information on this point; and if it were not accidentally that the fierasfer swallowed the walls of the compartment in which he was lodged, he ought rather to take his place among parasites. Though it lodges in the respiratory processes, as the learned professor at Wurtzburg asserts, the fierasfer may also be a messmate after the fashion of so many others which inhabit the neighbourhood of the rectum, in order the more conveniently to snap up those animals which are attracted by the odour.

The fierasfers are not the only fishes which seek assistance from the holothuriæ; a species lives at Zamboanga, to which the specific name of Scabra has been given, and in the stomach of which, says Mons. Johannes Müller, usually lives a myxinoid fish, called Enchelyophis vermicularis. Unfortunately, we are not told in what part of the stomach it resides; for all is stomach in these animals.

It is less degrading for a fish to ask assistance from one in his own rank. The Mediterranean offers a curious instance of this. Risso saw at Nice, at the commencement of this century, the monstrous fish known under the name of Beaudroie (the angler, or fishing-frog) lodging in its enormous branchial sac a fish of the family of the Murenidæ, the Apterychtus ocellatus. He is found there evidently under the condition of a messmate. Although the eels generally get their living easily, the Angler possesses fishing implements which are wanting in them, and

when both of them are immersed in the ooze, it carries on a fishery sufficiently abundant to enable it to share the spoil with others. This same angler lives in the northern seas, and there it harbours an amphipod crustacean, which until lately has escaped the vigilance of carcinologists. We shall speak of it further on.

Dr. Collingwood saw a sea anemone in the Chinese Sea, which was not less than two feet in diameter, and in the interior of which lodges a very frisky little fish, the name of which he could not tell.

Lieut. de Crispigny has observed a sea anemone (Actinia crassicornis) living on good terms with a malacopterygian fish, the Premnas biaculeatus. This fish penetrates into the interior of the anemone; the tentacles close round it, and it lives thus for a considerable time enclosed as in a living tomb. Mons. de Crispigny has kept these animals alive for more than a year, in order to make careful observations on them. A fish known by the name of Oxybeles lumbricoides has been also found in the Indian Seas, which modestly takes up his quarters in a star-fish (Asterias discoida). Another case of commensalism has been made known to us by Professor Reinhardt of Copenhagen. A siluroid of Brazil, of the genus Platystoma, a skilful fisherman, thanks to his numerous barbules, lodges in the cavity of his mouth some very small fishes, which were for a long time considered as young siluroids; it was supposed that the mother brought her progeny to maturity in the cavity of the mouth, as marsupials do in the abdominal pouch, or as some other fishes do. These messmates are perfectly developed and adult, but instead of living on the produce of their own labour, they prefer to instal themselves

in the mouth of an obliging neighbour, and to take their tithes of the succulent morsels which he swallows. This little fish has received the name of Stegophilus insidiatus. We see that in the animal world it is not always the great which take advantage of the little. Still, let us not be deceived; there are fishes in the latitude of the Island of Ceylon which really hatch their eggs in the cavity of the mouth, and we have seen some in the museum at Edinburgh, labelled with the name of Arius bookei. Louis Agassiz has made the same observation on a fish of the Amazon, which has also been recognised by Jeffreys Wyman. One fish wraps up its eggs in the fringes of its branchiæ, and protects them till they are hatched; another lays its eggs in holes hollowed out by itself in the steep banks of the river, and protects the young ones after they are hatched.

To hatch the eggs in the mouth is not more extraordinary than to hatch them in any other part of the body. The Sygnathidæ hatch theirs in a pouch behind the anus; and it is a curious circumstance that the females do not undertake this duty. The males alone carry their progeny with them. This recalls to our recollection that curious example of the birds known under the name of Phalaropes, among which the males only hatch the eggs. The female of the cuckoo abandons her eggs, and entrusts them to the female of another bird.

The cuckoo suggests to us the mound-making Megapode and the Talegalla of Latham, both of which inhabit Australia; these birds deposit their eggs in an enormous mass of leaves or grass, which grows warm by decomposition, and the temperature of which is great enough to hatch them. The young ones when they come

out of the egg are sufficiently developed to be able to provide for their own wants, and to do without a mother’s care.

To return to our animal messmates: let us notice the result of the observations of a learned and skilful naturalist who has rendered great services to ichthyology. Dr. Bleeker has described a still more remarkable association in the Indian seas; it is that of a crustacean, the Cymothoa, taking advantage of a fish known under the name of Stromatea; too imperfectly organized to fish for itself at large, but more skilful in snapping up all that comes within its reach, it makes its home in the buccal cavity of the Stromatea.

But of all crustaceans, the most cruel is the isopod named Ichthyoxena, which hollows out for itself and its female a large dwelling-place in the coats of the stomach of a cyprinoid fish. We will return again to these examples.

The Physaliæ, those charming living nosegays of the tropical regions, also give lodging in their cavities, and in the midst of their long cirrhi, to little adult and perfect fishes, belonging to the family of the Scombridæ, a family to which are attached the tunny and the mackerel. These sea-butterflies flutter away their indolent existence at the expense of their host. Voyagers tell us that they have seen them by dozens concealed in these animated festoons. Mons. Al. Agassiz has mentioned, in his illustrated catalogue, another fact, quite as extraordinary, observed in the Bay of Nantucket, in the United States; it relates to a nocturnal Pelagia (Dactylometra quinquecirra, Ag.) always accompanied, not to say escorted, by a species of herring. The two neighbours constitute

together an association which probably redounds to the advantage of both.

Without quitting our own sea-coast, we find an association of the same kind between young fishes (Caranx trachurus) and a beautiful medusa (Chrysaora isocela). This sea nettle often encloses several young specimens of Caranx, which we are surprised to see issuing full of life from the transparent bodies of these polyps. Indeed, it is not rare to find other fishes in the medusæ. Dr. Gunther, who has arranged with so much care the rich collection of fishes in the British Museum, has shown us some specimens of the Labrax lupus, and of the Gasterosteus, which had been obtained from the interior of different medusæ; and these associations have been also remarked by various distinguished observers, among whom we may mention Messrs. Sars, Rud. Leuckart, and Peach. The captain of the frigate Jouan, when in the Indian Sea, on October 26th, 1871, in 13° 20′ N. lat., and 60° 30′ E. long., that is to say, about 200 leagues to the west of the Laccadive Islands, saw, in very fine weather, the sea, which was at that time very calm, covered with medusæ, and the greater part of these were escorted by many little fishes of the genus Ostracion, the species of which he was unable to ascertain. It is probable that the school of medusæ set in motion certain animals which are eagerly sought after by the Ostracions.

The Pilot is a fish of which much has been recorded; fishing for it is one of the principal recreations of sailors during their long voyages. Some assure us that it snaps off the bait, without touching the murderous hook which threatens the shark; and as it never quits its companion, others have supposed that it lives on the

morsels abandoned by it. Neither of these suppositions is correct; and as the shark does not need its services to point out the danger, we must content ourselves with mentioning this curious association without endeavouring to explain it.

In fact, we have had the opportunity of examining many well-preserved specimens, the stomach of which contained potato parings, the carapaces of crustaceans, the débris of fishes, marine plants (fuci), and a piece of cut fish, which had evidently served as a bait. The pilot does not, therefore, live on the leavings of his companion, but on his own industry, and doubtless finds some advantage in piloting his neighbour. Through the great kindness of Dr. Gunther we have been able to make this interesting examination in the rich galleries of the British Museum. We desire to take this opportunity of expressing our gratitude to this learned man and to his illustrious colleagues, who have the direction of that vast establishment, which is ever open to those who labour for the advancement of science.

The pilot has sometimes been confounded with a very different fish, which does not merely remain in the neighbourhood of the shark, but establishes itself upon him, and moors himself to him by the aid of a particular apparatus, for a longer or shorter time; we may even say during the whole of the voyage. This is the Remora.

Is this fish the messmate of the shark to which he is attached? As in the case of the pilot, an examination alone could decide the question. We have opened at the British Museum the stomachs of several remoras of different sizes, and we have been able to ascertain that they also fish on their own account; their food was

composed of morsels of fish which had served as bait, of young fish swallowed whole, and of some remains of crustacea. The remora is simply anchored to his host, and asks from him nothing but his passage. He is contented, like the pilot, to fish in the same waters as the shark which transports him. Sailors, even now, are convinced that if any one of these remoras should attach itself to the ship, no human power could cause it to advance, and that it must of necessity stop. It is certain that the fishermen of the Mozambique Channel take advantage of this faculty, to fish for turtles and certain large fish. They pass through the tail of the remora a ring to which a cord is attached, and then send it in pursuit of the first passer-by which they consider worthy to be caught. This kind of fishing resembles in some degree the sport of hawking with falcons.

So extraordinary a being could not fail to attract the attention of those among the ancients who were students of nature. Pliny assures us that the remora was used in the preparation of a philtre capable of extinguishing the flames of love.

There must be many free animal messmates among insects, and entomologists should make them known; for example, many of them live with ants, as the Pselaphidæ and Staphylinidæ. Certain hairs of these insects, it is said, secrete a sweet liquid of which ants partake greedily. If we may believe a skilful observer, Mons. Lespès, there are some among them, as the Clavigers, which in exchange for the services which they render are fed by the ants themselves. We may also mention the larvæ of the Meloë, which seem to live as parasites, and the true nature of which was so long unknown.

The females of the Meloë lay their eggs near the ranunculus and other plants whose flowers are regularly visited by bees. After these are hatched, the larvæ ascend into the flowers and wait patiently till a bee takes them on his back, and carries them into the interior of the hive. This insect was formerly known under the name of the bee-louse, but this appellation is improper, for the bee is not the host of the meloë, but simply its beast of burden. According to recent observations, flies perform the same office for Chelifers, and certain aquatic and land coleoptera for several kinds of acaridæ.

In the class of animal messmates we find also a coleopterous insect that lodges in a manner similar to the paguri, of which we shall presently speak. The female of the Drilus, a species allied to glowworms, attacks the snail, and when it has devoured it, instals itself in the shell, to pass through its metamorphoses; when necessary, it frequently changes its shell and chooses successively more spacious lodgings. Like a true Sybarite, the drilus weaves a curtain of tapestry before the entrance of its habitation, and remains there peaceably surrounded by the vestment of its youth.

Remarkable examples of free messmates are found more especially among crustaceans. It is well known that this class includes lobsters, crabs, prawns, and those legions of small animals which serve as the police of the sea-shore, purifying the waters of the ocean of all organic matters, which otherwise would corrupt them. They do not, like insects, shine with variegated colours; their forms are hardy and varied, and they are often pleasing on account of the singularity of their movements. Professor Verrill has recently studied some of

these creatures, and has clearly shown how interesting they are, not only to naturalists, but to people in general.

Crustaceans and worms furnish the greatest number of paupers and infirm individuals; and a great many of them need the continual assistance of their neighbours to enable them to get their living. While other animals advance towards perfection as they grow older, it is far different with many crustaceans, and we should be tempted to refer to the vegetable kingdom many of them at the very period when they are approaching the adult condition. Cuvier placed all the class of cirrhipedes among the mollusca, and the lernæans among the worms. Many of these animals which are but indifferently adapted to live without help from others, have recourse to benevolent neighbours; from one they seek only shelter, from another a part of his booty, from a third both an asylum and protection. They are often reduced to a mere skin; everything else has disappeared, and there remains no proper organ except that which is necessary for the reproduction of the species. Corpulent, blind, impotent, legless cripples, their existence is more precarious than that of those miserable mutilated beings found in our cities; they only live on the blood of the neighbour which gives them an asylum. Yet when they first quit the egg they are all free; they frisk, they swim with the rapidity of lightning, and at the close of life we find them deformed, and crouched in some living refuge, as if a foul leprosy had atrophied within them all the organs which served as a means of communication with the outer world. Parasites and messmates, furnished at first with the same kind of limbs and the

same habits, can sometimes only be distinguished from each other when we have made our observations on them in their first swaddling clothes. The child has given a clue to the history of the old man.

We will not examine these animals in all the details of their private life, and yet we are strongly tempted to confess to our readers some of the indiscreet acts of which we have been guilty, in watching them while changing their dress. Notwithstanding their shyness and their desire to escape observation during the moulting period, we have more than once made observations on them while quitting their garment which has become too small. The old tunic generally splits down the back, and falls off all in one piece as it gives the animal egress. The crustacean is extended quite soft and supple by the side of its rigid carapace.

Of all the free crustacean messmates, one of the most interesting, though among the smallest of them, is a tiny crab, about as large as a young spider, which lives in mussels, and which has been often accused, though evidently wrongfully, as the cause of the indisposition so well known by those who are fond of this mollusc. Very many of them have been seen within the last few years, and yet accidents have been very few. The mussels themselves are guilty; they produce on some persons an injurious effect, through idiosyncracy. We have at least a word to serve as an explanation, and at present we must content ourselves with it.

Under what conditions do those crabs, called by naturalists Pinnotheres, and which we do not find elsewhere, inhabit mussels? Are they parasites, pseudo-parasites, or messmates? It is not a taste for voyaging

which tempts them, but the desire of having always a secure retreat in every place. The pinnothere is a brigand who causes himself to be followed by the cavern which he inhabits, and which opens only at a well-known watchword. The association redounds to the advantage of both; the remains of food which the pinnothere abandons are seized upon by the mollusc. It is the rich man who instals himself in the dwelling of the poor, and causes him to participate in all the advantages of his position. The pinnotheres are, in our opinion, true messmates. They take their food in the same waters as their fellow-lodger, and the crumbs of the rapacious crabs are doubtless not lost in the mouth of the peaceful mussel. There is no doubt that these little plunderers are good lodgers, and if the mussels furnish them with an excellent hiding-place and a safe lodging, they themselves profit largely by the leavings of the feast which fall from their pincers. Little as they are, these crabs are well furnished with tackle, and advantageously placed to carry on their fishery in every season. Concealed in the bottom of their living dwelling-place (a den which the mussel transports at will) they choose admirably the moment and the place to rush out to the attack, and always fall on their enemy unawares. Some of these pinnotheres live in all seas, and inhabit a great number of bivalve molluscs. The northern seas contain a large species of Modiola (Modiola Papuana) which is especially found in deep and almost inaccessible parts, and which always encloses a couple of pinnotheres about the size of a hazel-nut. We have opened hundreds of these modiolæ, and we have never met with any without their crabs. We have long since deposited

some specimens of these pinnotheres in the galleries of the Natural History Museum at Paris.

The large mussel, which furnishes fine pearls (Avicula margaritifera), lodges also pinnotheres of a particular species by the side of another messmate more allied to a lobster than a crab. It is not even impossible that these crustaceans, with other messmates or parasites, contribute to the formation of pearls, since these gems, so highly prized in the fashionable world, are only the result of vitiated secretions, and are usually the result of wounds.

We also meet with a little crab (Ostracotheres tridacnæ, Ruppel) in the acephalous mollusc, whose immense shell sometimes serves as a vessel for holy water; and it lives doubtless in many other bivalves which have not yet been examined.

Dr. Léon Vaillant has written a very interesting memoir on the Tridacnæ, and informs us that the crab takes shelter in their branchial chamber. Therefore, since the molluscs live only on vegetable substances, while the Ostracotheres feed entirely on animal matter, Mons. Vaillant supposes that the latter take their choice of the food as it enters, and seize on its passage that which suits them best. Mr. Peters, during his abode on the coast of Mozambique, studied a great many of these acephala and pearl-mussels, and found their interior inhabited by three crustacean decapods, a pinnothere, and two macrouræ allied to the Pontonia, to which he has given the name of Conchodytes; the Conchodytes tridacnæ inhabits the Tridacna squamosa; the Conchodytes meleagrinæ, as its specific name indicates, lives in the shell of the pearl-mussel.

Professor Semper has recently observed pinnotheres in holothurians at the Philippine Isles, and Mons. Alphonse M. Edwards has described some from New Caledonia (P. Fischerii); so that these little crabs, the friends of the molluscs, are known in both hemispheres.

Do not these conditions seem to authorize the conclusion that the same thought has presided over the appearance of all living creatures; that they have all come into existence, not according to the chance arrangement of surrounding media, but according to the laws established from the very origin of all things?

The shell which lodges both these pinnotheres, in the Mediterranean as well as the Atlantic, is a large acephalous mollusc, known under the name of Jambonneau (a small ham or gammon), and which, according to Aristotle, harbours two different kinds of messmates. This illustrious natural philosopher also described a Pontonia (Pontonia custos, Guérin—P. Pyrrhena, M. Edw.) about an inch and a half long, of a pale rose colour, more or less transparent, and which lives with its companion, the pinnothere, in the cavity of the Pinna marina. This is the same animal which a naturalist of the last century named the Cancer custos.

We have wished to ascertain whether Pliny knew these crustaceans. He has spoken of them in the following terms:—“The Chama is a clumsy animal without eyes, which opens its valves and attracts other fishes, which enter without mistrust, and begin to take their pastime in their new abode. The pinnothere seeing his dwelling invaded by strangers, pinches his host, who immediately closes his valves, and kills one after another these presumptuous visitors, that he may eat them at his leisure.”

Cuvier did not believe that the pinnothere brought any food to the mollusc, since the latter, in his opinion, lives entirely on sea-water.

Other zoologists regard the pinnothere as an intruder whom chance has brought into this mysterious position. Others again consider mussels as acquaintances possessed of a very curious disposition, and that having no eyes, they have interested in their fate this little crab, which is perfectly provided with eyesight. In fact, in common with other crustaceans of his species, he carries on each side of his carapace, at the end of a movable stalk, a charming little globe, provided with some hundreds of eyes, which he can direct upon his prey, as the astronomer turns his telescope on any point of the firmament. These later naturalists consider, in fact, their crab as a living journal which supplies his host with the news of the day. Rumphius, a Dutchman, the first who described the animal of the nautilus, also understood the habits of pinnotheres. In his “Amboinche Rariteit Kamer,” published in 1741, he says that these crustaceans inhabit always two kinds of shellfish, the Pinna and the Chama squamata. According to him, when these molluscs have attained their growth, one pinnothere (one only at least in the Chama) lives in their interior and does not abandon its lodging till the death of its host. Rumphius regards this crustacean as a faithful guardian, fulfilling the duties of a door-keeper. In 1638 he found actually two sorts of keepers: by the side of a Brachyuron, carrying an embossed buckler, slender in front, he discovered a Macrouron of the length of his finger-nail, of a yellowish orange colour, semi-transparent, with white and very slender claws. It is

without doubt the same animal that Mons. Peters, of Berlin, found on the coast of Mozambique, and of which we have spoken before.

A little crab is known to live near the coast of Peru (Fabia Chilensis, Dana), which exists under somewhat different conditions. He chooses, not a bivalve mollusc, but a sea-urchin (Euriechinus imbecillus, Verrill), and lodges in the intestine, near its termination, so as to seize as they pass by all those living creatures which are attracted by the odour. Doubtless, the delicacy of our sense of smell is disgusted by such a mode of seeking food; but this predilection may have a reason with which we are not acquainted. There are a considerable number of other species which live under similar conditions.

On the coast of Brazil, my son found two couples of crabs in the tube of a very long annelid, narrow at the ends, and wide in the middle. The tube was too small at the end to allow them to escape. These crustaceans had, no doubt, penetrated thither before they had attained their full size.

A crab of the family of the Maidæ conceals itself in the substance of a polypidom very common in the Viti Islands, in company with a gasteropod mollusc, and both of them assume the exact colour of the polypidom. This is a new kind of mimicry. This crab is known by the name of Pisa Styx, the gasteropod is a Cypræa, the polyp is the Melithea ochracea. A decapod crustacean, the Galathea spinirostris, seeks for a Comatula, the colour of which it exactly imitates, and with which it lives on the most friendly terms.

The holothuriæ, of which we have already spoken, appear to afford an abode to many animals: independently

of the Fierasfer, the Holothuria scabra of the Philippine Islands regularly lodges in its interior a couple, and sometimes, though rarely, a greater number of pinnotheres belonging to two distinct species. They choose this domicile at an early period, and must be highly delighted with this obscure abode, since they are seen no more, and when they have once entered never quit this living cavern. This observation is due to Professor Semper, who has made us acquainted with so many curious facts of the China Sea and the Pacific Ocean. In the midst of the slender branches of a coral of the Sandwich Islands, the Pæcilopora cæspitosa of Dana, there lives a little crab (Hopalocarcinus marsupialis, Stimpson), which is at last completely enclosed by the vegetation of the coral. It only keeps up sufficient communication with the exterior to enable it to procure food. The coral, however, furnishes it nothing but a resting-place in the midst of its tissues.

Among the Philippine Islands, also, a brachyurous crustacean lives in the branchial cavity of one of the Haliotidæ, and another on the body of a holothuria. On the coasts of Brazil, F. Müller, during his abode at Desterro, saw some Porcellanæ inhabiting star-fish, not as parasites, as had been supposed, but as true messmates. A crustacean possessed of but little generosity is the Lithoscaptus of Mons. Milne-Edwards. Provided with beak and claws for the purpose of attack, it instals itself, sad to say, in the pantry of a medusa, and instead of making use of its own weapons, takes advantage of the perfidious nematocysts of its acolyte, in order to live quietly at his expense.

Under the name of Asellus medusæ, Sir J. G. Dalyell

has made us acquainted with another messmate of the medusæ which greatly resembles an Idothea.

Another kind of commensalism is that of the Dromiæ. These crabs are of the ordinary size, and lodge, from their earliest youth, under a growing family of polyps, which increases with them. This colony has for its principal foundation a living Alcyonium, which covers the carapace, and as it develops, adapts itself perfectly to all the inequalities of the cephalothorax; one might consider it an integral part of the crab. Sertulariæ, Corynes, Algæ, develop themselves on this Alcyonium, and the Dromia, masked by this living rock which it carries on its shoulders like the fabled Atlas, marches gravely in pursuit of her prey. She has no fear of arousing the attention of her enemies. The greatest vigilance cannot prevent the sudden attack of these dangerous neighbours. There is in the Mediterranean a species which sometimes comes to our coast. They are also known in the Indian Seas and in the Northern Pacific. Rumphius named the dromia Cancer lanosus; it is, said he, a crab which carries grass or moss on its back. It is also mentioned by Renard. Dana has observed a sea-anemone covering a crab in the same manner as the Alcyonium does the dromia, and which is not less dangerous. The mode of life of this anemone has procured for it the name of Cancrisocia expansa. In the north of California, a crab (Cryptolithoides typicus) covers itself in the same manner with a living cloak which hides it from view, and under cover of which it surprises those whom it attacks. It has already cleared the ground of its prey before any alarm has been given to the neighbourhood.

We should perhaps speak here of an association of another kind, the nature of which it is difficult to ascertain; I refer to the little crab, the Turtle Crab of Brown, which is met with in the open sea on the carapace of turtles, and sometimes on sea-weeds. It may be supposed that it takes advantage of the carapace of its neighbour, in order to transport itself at little expense into different latitudes, and it is asserted that the sight of this crustacean gave confidence to Christopher Columbus, eighteen days before the discovery of the New World. Besides this animal, a whole society chooses this movable habitation: in addition to the cirrhipedes we also find the Tanaïs, which is not, however, condemned to live there always.

The macrourous decapods are more rarely found as messmates, but still a Palæmon is sometimes seen on the body of an Actinia, according to Semper, and another in the branchial cavity of a Pagurus. But that which is more generally known, is the presence in the Euplectella aspergillum of the palæmon which lodges in this fairy palace. It is probable that the Euplectella of the Atlantic, recently observed near the Cape Verd Islands by the naturalists on board the Challenger, also conceals this crustacean in its interior. We may also allude here to the Hypoconcha tabulosa, a crab whose carapace is too soft to allow it to venture out undefended, and which covers itself with the shell of a bivalve mollusc.

Among the various associations of this kind, none is more remarkable than that of the soldier-crabs, so abundant on our coasts, and called by the names of Bernard the Hermit and Kakerlot by the Ostend fishermen. It is well known that these crabs are decapod crustaceans,

very like miniature lobsters, which lodge in deserted shells, and change their dwelling-place as they grow larger. The young ones are content with very little habitations.

The shells which give them shelter are such as have been shed, which they find at the bottom of the sea, and in which they conceal their weakness and their misery. These animals have an abdomen too soft to bear the dangers which they meet with in their warfare, and that they may be less exposed to the claws of their numerous enemies, they take shelter in a shell which serves at the same time both as a dwelling and a buckler. Armed cap-à-pie, the soldier-crabs march boldly on the enemy, and know no danger, since they always have a secure retreat.

But this animal does not live alone in this asylum. He is not so much of an anchorite as he appears to be, for by his side an annelid usually instals himself as a messmate, which forms with the Pagurus one of the most terrible associations that are known. This annelid is a long worm, like all the nereids, whose supple and undulating body is armed along its sides with arrows, lances, pikes, and poniards, the wounds of which are always dangerous. It is a living panoply which glides furtively into the enemy’s camp without giving the alarm.

When a pagurus is on the march it resembles a nest of pirates, who never cease their exploits till all has been ravaged around them. This shell is so innocent in its appearance, that it introduces itself everywhere without provoking the least suspicion. It is usually covered with a colony of Hydractiniæ, and in the interior, Peltogasters,

Lyriopes, and other crustaceans often establish themselves. The paguri are not messmates of an ordinary kind, for they inhabit only a deserted shell. They are spread over all seas. They are found in the Mediterranean, the Northern Sea, on the coasts of the Pacific, of New Zealand, and of the East Indian islands: thirty species and even more have been inserted in the catalogue of crustaceans.

Naturalists have given the name of Cenobitæ to some pagurians inhabiting the seas of warmer latitudes; these have an abdomen like the pagurus, antennæ like the Birgus, and like it they inhabit shells. The Cenobita Diogenes is a species found in the Antilles.

Other pagurians, the Birgi, grow very large, and conceal their abdomen no longer in a shell, but in the crevices of the rocks, as lobsters do at the moulting time, to protect their body while deprived of their defensive armour. In the East Indies they remain on land, and even climb into trees. They have so much strength in their pincers, that Rumphius relates of one of these crustaceans, that, while stretched on a branch of a tree, it raised a goat by the ears.

Side by side with the pagurians which instal themselves in a shell with thick and completely opaque walls, we recognize crustaceans of the order of amphipods, the Phronimæ, which choose for themselves not an abandoned hovel, but a veritable crystal palace, and take possession of it without inquiring whether or no it is inhabited. The daylight penetrates through the walls of their dwellings, and it can scarcely be discerned in the water whether or no their body is protected by a covering. They usually take the dwelling of a Salpa, a

Beroë, or a Pyrosoma, and from within this lodging they give themselves up to the pleasures of fishing.

The Phronima sedentaria which lodges with the salpa seems to be scattered over the warm seas of both hemispheres. For the honour of the species, the females alone seek the assistance of their neighbours, without at the same time abandoning their characteristic robe. The sexes differ little from each other except in size, in the abdomen, and in the antennæ. Maury has described certain amphipod crustaceans which also inhabit the Salpæ.

Another phronima described by Professor Claus, the Phronima elongata, lives in the same manner; but instead of occupying a living house, it generally seeks an empty lodging, in which it establishes itself like a pagurus.

The “Bernard the Hermit” of the Marseillaise fishermen, the Pyades, becomes the messmate of an anemone which Dugès has called Actinia parasitica. According to the observations of the learned professor at Montpelier, the mouth of this anemone is always situated opposite to that of the crustacean, to take advantage of the morsels which escape from his pincers. Both of them profit by this association; and the opening of the shell is prolonged by a horny expansion furnished by the foot of the actinia.

On the coast of England lives another soldier-crab (Pagurus Prideauxii), which has as its principal messmate a sea anemone called Adamsia, which Mons. Greeff found at the island of Madeira. This pagurus is especially remarkable for the good understanding which exists between himself and his acolyte—he is a model Amphitryon. Lieut.-Col. Stuart Wortley has watched it in its

private life, and thus relates the result of his observations: this animal after he has fished, never fails to offer the best morsels to his neighbour, and often during the day, ascertains if it is not hungry. But more especially when he is about to change his dwelling, does he redouble his care and his attention. He manœuvres with all the delicacy of which he is capable, to make the anemone change its shell; he assists it in detaching itself, and if by chance the new dwelling is not to its taste, it seeks another until the Adamsia is perfectly satisfied. This association is not confined to the union of a decapod with a nereid and an actinia; a curious cirrhipede often establishes itself on the body of the pagurus, and on the outside of the shell we generally find a colony of polyps, of a rose or yellow colour, which extend like a living carpet round this habitation. Thirty-six years ago we have given the name of Hydractinia to these polyps, which were till then entirely unknown to naturalists, and which form habitually a double overcoat for the paguri, if I may employ the expression of my learned colleague, Mons. Ch. Desmoulins.

In the Mediterranean lives the Perella di mare of the Italian fishermen, the Reclus marin of the Marseillaise; this Alcyonium ought, by its manner of life, to be placed near the Hydractiniæ, and has been carefully studied by Mons. Ch. Desmoulins. It is the Alcyonium (Suberites) domuncula of Lamarck and Lamouroux.

The abdomen of these paguri is not only sheltered in a shell, but habitually visited by isopod crustaceans, described under the names of Athelea, Prosthetes, and Phryxus, which have entirely lost the livery of their order.

In the same association we also find the Liriope, a little isopod crustacean, of which much has been said, but which for a long time obstinately resisted all attempt at observation.

This latter personage is an isopod crustacean, of moderate size, which chooses the Peltogaster as a place of abode, after having undergone a very curious regressive metamorphosis. In fact, the young lyriope has at first its little feet like other isopods, but in the adult state, the female loses her antennæ, and changes her buccal as well as her branchial appendages, so as to assume a different appearance. Several naturalists have already endeavoured to give the life-history of this singular Bopyrian. The illustrious Rathke of Königsberg discovered it; Professor Lilljeborg, of the University of Upsal, gave the first account of it; and finally Professor Steenstrup of Copenhagen made known its true origin. In short, the Lyriopes are Bopyrian Isopods, living on cirrhipedes (Sacculinideæ) as real messmates, if not as parasites; the male preserves his dignity and his prestige, but the female strips herself of all the attributes of her sex, and descends to the lowest degree of servitude.

Faujas de Saint-Fond has mentioned a fossil hermit-crab as found in the mountain, St. Pierre de Maestricht; but he called by this name a crustacean of the genus Callianassa and not a pagurus. These Callianassæ are always completely isolated in the chalk, and it is probable that they have no other domicile than the sand or ooze at the bottom of the sea, in which they hollow out galleries for themselves. Lobsters act in the same manner after moulting. The Gebiæ live like the Callianassæ,

hidden in the mud. The Limnaria lignorum and the Chelura terebrans dig out a retreat for themselves in wood, like the Teredines.

We have just seen that the higher crustaceans, with their well-mounted eyes, their enormous antennæ, and their formidable pincers, are not all of them the great lords they pretend to be; more than one of them has to hold out its hand and to accept humbly the assistance of its neighbours.

In the group of isopod crustaceans we find many necessitous beings, which, too proud to ask for food, are contented to take their place on some fish which is a good swimmer, which they abandon as soon as their interest demands it; if their host conducts them to regions that do not suit them, or if they have otherwise to complain of him, they give him up, and begin their maritime peregrinations with a fresh colleague. They always preserve all their fishing tackle and their sailing gear, and the female does not change her dress any more than the male. We have to notice that these crustaceans often identify themselves so entirely with their host that they seem to be a portion of him, and even to assume his peculiar colour. This is not a sign of servility, but a means of passing unobserved, and of escaping from the sight of the enemy that is watching them. Naturalists have given the name of Anilocræ to some of these free messmates.

Any one who has remained for some time on the coast of Brittany, especially at Concarneau, and who does not look with indifference on the many superb fishes which are taken every day, cannot fail to have been struck with the presence of a rather large crustacean,

which clings to the sides of several kinds of Labra, especially the smaller species. This crustacean is an Anilocrian so common that we can scarcely imagine it to have escaped the attention of any naturalist. Nevertheless, no work makes mention of the regular attendance on the Labra by the Anilocra, which bears, we know not why, the specific name of Mediterranean. Rondelet was probably acquainted with it, when he spoke of the fish-lice, which do not derive their birth from these fishes, but from the sea mud. We often see males by the side of females on the same individual.

Some years ago a school of large cetaceans, known under the name of Grindewhalls or Globicephalæ were pursued in the Mediterranean, and those which were captured contained in the cavity of their nostrils, isopods closely allied to the Cirolana spinipes, if not identical with it. Till then the isopods had only been found on sea fishes; fresh-water fish are not, however, entirely exempt; in fact, a species of Œga (Œga interrupta of Martens) has just been found on the skin of a fresh-water fish of Borneo, the Notopterus hypselonotus. This same genus includes a species (Œga spongiophila) which lives in the magnificent sponge, the Euplectella. We know also a certain number of isopods which prefer the interior of their neighbour’s body, and instal themselves in the cavity of the mouth, either to fish at the same time as their host, or to seize the food on its passage; others are of such a cruel nature, that they make no scruple to establish themselves in the stomach of a peaceable white fish. Without injuring any important organ, they penetrate in couples between the intestines, and, concealed in this retreat, they seize by the narrow

entrance door, which they keep half open, all the little animals which are sufficiently bold to pass by. The cruelty of these beings knows no bounds. To instal themselves conveniently, they pierce the body of their host, skilfully open his stomach, and live there as Sybarites; their lodging is in future assured to them, and their fate is bound up with that of their host. Dr. Herklots, who has unfortunately been recently lost to science, communicated in 1869, to the Academy of the Netherlands, a very interesting memoir on two crustaceans of a new species, the Epichtys giganteus, which lives on a fish of the Indian Archipelago, and the Ichthyoxenus Jellinghausii, which lodges in a fresh-water fish of the Island of Java. It is to the latter that we refer here, and it seems that in this species we are approaching the limits at which commensalism commences.

The Cymothoes constitute another category of very interesting Isopods; they lodge with their female in the cavity of a fish’s mouth. Dr. Bleeker, who has so successfully explored the Indian seas, obtained more than twenty species of these; but unfortunately he has not made a note of the fishes which harbour them. He has, however, made one exception with regard to a fish from the roadstead of Pondicherry, which is two feet long, and is called a Bat. It is known to naturalists under the name of Stromatea Nigra; its flesh is much esteemed, and it carried in its mouth a Cymothoe called by Dr. Bleeker Cymothoe Stromatei. A cymothoe has also been observed in the mouth of an Indian Chetodon. De Kay found one in a Rhombus in the United States, and De Saussure saw another at Cuba; and lately, Mons. Lafont discovered one in the Bay of Arcachon, on

the Boops, and on the Trachina vipera. These cymothoes are about fifteen millimetres in length, and often fill all the cavity of the mouth. The most curious of all is that which is found in the mouth of the flying-fish, a kind of herring with elongated fins, which it uses as wings to rise into the air, when too closely pursued in the water. My son, when examining these fishes, in his passage from Cape Verd to Rio de Janeiro, found in the cavity of their mouth an enormous female, firmly wedged in the branchial arches, with its head inclined outwards, and the male, which was rather smaller, installed at her side. Their dwelling thus by pairs, as well as the entire conformation of the animal, plainly shows that these crustaceans make themselves at home, and live as true messmates. Cunningham has given them the name of Ceratothoa exoceti. A short time since, these Cymothoes were only known on marine fishes, but it appears from recent observations, that fresh-water fish are far from being exempt from them. Mons. Gertsfeld has recently noticed some on the Cyprinus lacustris of the river Amour, and another in the Rio Cadea in Brazil, on a Chromida. Other isopods also resort to fishes, and to animals of their own class, but they live as true parasites, and change their form as soon as they have chosen a resting-place. We shall return to this subject again. Some which are very common on prawns, are known under the name of Bopyrus.

An interesting division of amphipods have received the name of Hyperinæ. These crustaceans generally swim with facility, but walk with difficulty. They therefore usually have recourse to fishes, or even to medusæ, in order to gain support. We find on our own coasts the

Hyperina Latreillii, lodged in the superb Rhizostoma, which regularly appears in the later season of the year on the coast of Ostend; and a long time since, in 1776, O. F. Müller gave to a species of this genus the name of Hyperina medusarum. Mr. Alexander Agassiz once found a Hyperina on the disc of an Aurelia. The medusa, when extended, forms for them a balloon with its parachute, which supports and conveys them with greater or less rapidity. Professor Möbius has but lately remarked the presence of Hyperina galba, Mont., in the Stomobrachium octocostatum, Sars, a small species of medusa which appears in the Bay of Kiel in October and November. This naturalist supposes that these messmates at first inhabited the Medusa aurita, and then migrated into this species.

Besides these, there are Gammari, which, according to Semper, live in the Avicula meleagrina (pearl mussel), and are perhaps the principal manufacturers of fine pearls. The immense buccal cavity of the fishing-frog (Lophius piscatorius) is the abode in the Mediterranean of an Apterychta, and in the Northern Ocean of a curious amphipod of the ordinary size of the Gammarus, which takes a voyage without expense, and with no fear of wanting provisions. My son discovered it at Ostend, and proposes the name of Lophiocola to distinguish it. The Gammari give lodging themselves to a great quantity of parasites, which they must introduce into the bodies of those to whom they serve as food. It has been long known that whales have lice, to which naturalists have given the name of Cyami. They are found on the whales of both hemispheres, and on some other cetaceans. It is very remarkable that they are

seen on the true whales of the north and of the temperate regions, on the Megaptera, and on several Catodonta, and that none are found in the Balenoptera. Mr. Dall has just noticed some on the singular Grey Whale of California. In general, we may say that each cetacean which harbours them, has its own species. Are they parasites or messmates? If we are to believe Roussel de Vauzème, they feed on the skin itself of the whale, the remains of which, it is said, are found in their stomach. According to this naturalist, the parts of the mouth are not adapted for suction, and the stomach contains ruminating apparatus. We think that a fresh examination is necessary before this question can be determined. The Cyami seem to us to live on the whale, as the Arguli and the Caligi do on fish; and if these living creatures derive their nourishment only from the mucous products secreted by the skin, we may ask whether they ought not to be classed in a separate category, for they ought not to figure on the list of paupers. We have found the orifice of the Tubicinella covered with cyami of every age, and their abundance in this place seems to indicate that their food was not supplied to them by the skin of their host. Mons. Ch. Lutken has recently published a very interesting monograph on these curious animals; according to him the Cyamus rhytinæ, which was thought to proceed from a piece of the skin of a Stellerus, appears to have been found on the skin of a whale.

The Picnogonons, the nature as well as the kind of life of which has been so long time problematical, deserve to be ranked among messmates, at least during their youth; in fact, after being hatched, they live on

the Corynes, the Hydractiniæ, and other polyps, while at a later period they frequent molluscs or higher classes; Allman mentions the case of a Phoxichilidium coccineum lodged in a Syncoryne.

There are, perhaps, many other crustaceans which, placed among messmates, like the Pandarus and others, would have a right to claim a further inquiry. It is a fact that they are never seen except on the skin of their host, where they are always visible, preserve their colours entire, and never change their costume for the undress of a parasite. The Pandari live especially on the Squalidæ. Some which are found in our seas are of rare elegance of form. We must, perhaps, place among messmates the crustacean which Siebold found in the Adriatic, at Pola, on the belly of the worm Sabella ventilabrum, and it is not impossible that the Staurosoma observed by Will on an actinia, should have its place here rather than among the parasites.

A Rotifer without vibratory ciliæ, the Balatro calvus of Claparède, lives as an epizoon on the same annelids which lodge the Albertia in their interior. The Darwinists, observes Claparède, will not fail to remark the presence of these Rotifers of the genus Albertia in the interior of the animal, and of the genus Balatro on the exterior. The parasite Balatro, like a shadow, never quits his Mecænas, says the learned naturalist of Geneva; who has observed it on the limicolous Oligochæts of the Seime, in the Canton of Geneva.

The Nebalia of Geoffroy is an interesting crustacean, abundant on the coast of Brittany. This charming animal gives lodging habitually to a messmate which Mons. Hesse considered as an animal allied to the

Histriobdellæ, but which is only an imperfectly described Rotator. We believe that it is the same animal to which Professor Grube has given the name of Seison nebalia. It appears to assume the aspect of the Histriobdellæ, and may perhaps be adduced as an example of mimicry.

The molluscs, whatever their name may imply, are those which show the most independence among all the inferior ranks of animals; not only are they contented with the slowness of their pace and the wretchedness of their food, but they only very rarely seek help from their neighbours. It is not, however, uncommon to find some living among corals, which have even been designated coralligenous molluscs. There exists a group of Gasteropods, the Eulimæ, which lodge in certain Echinoderms, and in every respect deserve to be classed among messmates; it was a long time before the relation which exists between them and the animals which shelter them had been thoroughly appreciated. Dr. Gräffe found one species, the Eulima brevicula, on the Archaster typicus of the Uvea Islands, in the Pacific Ocean. The molluscs, known by the name of Stylifer, have the same mode of life; they have been observed in the Asteriæ, the Ophiuræ, the Comatulæ, and even in the Holothuriæ; and as they inhabit the digestive cavity of these animals, it was believed that they frequented them as parasites. This was the opinion expressed first by d’Orbigny, and adopted by most naturalists. Professor Semper found some in the skin of a holothurian (Stichopus variegatus), which he considered incapable of nourishing themselves otherwise than at the expense of their host. However this may be, these molluscs,

ranged alternately among the Phasianellæ, the Turritellæ, the Cerithia, the Pyramidellæ, the Scalariæ, the Rissoairia, or in a distinct family, seem to belong rather to messmates than to parasites. We meet with Stylifers at the entrance of the mouth (Montacuta); more frequently they prefer, like the Fierasfers, to lodge themselves deeply in the digestive cavity in the midst of the débris of the prey. The Melania (M. Cambessedesii, Risso), which Delle Chiaie found in the Bay of Naples, on the foot of some comatulæ, belongs probably to this group of molluscs.

Among the gasteropod molluscs which are not able to maintain themselves, we may mention another, a curious parasite, which instals itself in one of the rays of a star-fish, and whose presence is revealed by a swelling which is not produced in the other rays. This mollusc has received the name of Stylina.

The molluscs which are the most remarkable from the point of view from which we are now considering them, are the Entoconchæ; they live in Enchinoderms, and it was thought for a while that we could see in them an example of the transformation of one class into another. Some years since J. Müller found in a Synapta from the Adriatic, tubes with male and female organs, without any other apparatus, and in these tubes appeared eggs, whence this great physiologist saw molluscs proceed, with a helicoid shell, similar to that of a small natica; he gave them the name of Entoconcha mirabilis. Professor Semper has since discovered another species of these, which he has dedicated to the illustrious physiologist of Berlin, and which he found attached to the cloacal sac of the Holothuria edulis.

The true relation between these molluscs and the holothurians remains to be discovered, and how the entoconchæ become at last simple sexual tubes. At present we must admit that it is the result of a retrogressive development like that of the peltogasters, which, like them, lose all the attributes of their class. They ought, perhaps, to be placed farther on, among parasites.

Some years since, some molluscs were observed which have compromised more or less the dignity of their class. Gräffe cites a species of the genus Cypræa, which one would certainly not expect to find in this category; it lives among the Viti Islands, in the compartments of the Milithæa ochracea. We have referred to it before. Naturalists have given the name of Melithæa to a very beautiful polyp which forms colonies of two or three metres in height. Mons. Steenstrup, with that perspicacity which discerns the most complex phenomena, has also described Purpuræ which live as messmates with the Antipathes and the Madrepores. Quite recently, indeed, Mr. Stimpson has observed in the port of Charleston, a gasteropod mollusc, similar to a Planorbis (Cochliœlepsis parasitus) which lives as a messmate in the body of an annelid (Ocœtes lupina).

It is not the same with a mollusc called Magilus, which naturalists considered for a long time to be the calcareous tube of an annelid. All conchologists know the shell of the Magili, so valued by collectors. This gasteropod when young takes up its lodgings in the substance of a madrepore which grows more quickly than he, and in order not to die, stifled in this living wall, he constructs a calcareous tube similar to the shell, of which it appears to be the continuation, and which allows it

to procure for itself water, air, and food. The animal, protected by the madrepore, can do without its calcareous mantle, and only shows the end of the tube at the outside. It is this organ which sustains the struggle against the exuberant growth of the polyp, since it is by means of it that the mollusc obtains nourishment. The Magilus is like an oyster which is living in contact with a bank of mussels, with this difference, that the oyster almost always succumbs, while the magilus is always victorious in the struggle. We might also cite as well as the Magili, some Vermeti, certain Crepidulæ and Hipponices, which struggle with the same success against those which pilot or receive them.

As there exist parasites which only depend on others during their youth, so there are messmates which are completely independent when fully grown. Jacobson, of Copenhagen, wrote, in or about 1830, a memoir to show that the young bivalves which are found in the external branchial processes of the Anadontæ are parasites, and he proposed for them the name of Glochidium. Blainville and Duméril were charged to make a report on this memoir, which the author had sent to the Académie des Sciences. But his opinion had not many supporters, and it is now thoroughly known that the young anodonts differ considerably in their early and their full-grown state. During their stay in the branchial tubes, each young animal carries a long cable which descends from the middle of the foot, and serves to attach the anodont to the body of a fish, and yet permits it to move to a certain distance.[1] In fact the young anodonts have,

not like the other acephala, vibratory wheels in order to move themselves; they are conveyed in this manner by their neighbours. There are also messmate acephala, as the Modiolaria marmorata, which lodge on the mantle of ascidians. Professor Semper found attached to the skin of a Synapta similis, a mollusc which possesses a peculiarity rare among these animals, that of carrying its shell in the interior and not on the outside.

There are few animals so infested with parasites as the Ascidians in general. Not only does their surface sometimes become a microcosm, as the name of one Mediterranean species indicates, but even in the substance of their testa lodge Crenellæ and other molluscs and polyps, which choose by preference to place their dwelling there. There are also Annelids which hollow out galleries in their interior, Lernæans which establish themselves in their respiratory cavity, Nematodes, Pycnogonidæ, Ophiuræ, and many others besides. Mons. Alfred Giard has described several Amphipods and Isopods which establish themselves on Tunicates. One cannot say that there is always such a complete agreement between animals of such different kinds, for Mons. Alfred Giard gives examples of grave disagreements which he has seen break out, and which have caused the death of several among them.

Another association is that of a gasteropod with one of the acephala. In the environs of Caracas lives an Ampullaria (Crocostoma) which lodges in the umbilicus of its shell another mollusc, the only fluviatile species of those countries, called the Sphaerium modioliforme. We have every reason to suppose that the Sphaerium lives on good terms with the Ampullaria, since they are usually found associated.

The Bryozoaria, the animal mosses, establish themselves on all solid bodies at the bottom of the sea, like true mosses on stones or on trees. One species, a Membranipora, is usually found on the common mussel. These animals are of small size, group themselves in colonies on the surface of shells and of polyparies, or even on crustaceans, and form by their union a fine kind of lace, the dazzling whiteness of which often comes out sharply on the varying and glittering colour of the shell. This is because each animal lodges in a cell which is not larger than the head of a pin, and all the cells of a colony are grouped together with the symmetrical regularity of the façade of a Gothic building.

Many Bryozoaria live in such a manner that it is impossible to say whether they are messmates, or have installed themselves by chance in a hiding-place for which they have no predilection. A charming bryozoon is developed in abundance on the carapace and the claws of the Arcturus Baffini, on the coast of Greenland, and propagates itself with extreme rapidity. On a single Arcturus we have found, scattered over its claws by the side of each other, Balani, Spirorbes, Sertulariæ, and vast colonies of Membranipora. One can see, merely by this example, the great zoological riches of the polar seas.

Certain annelids off the coasts of Normandy and Bretagne are the abodes of a bryozoary known under the name of Pedicellina, or Loxosoma. This interesting animal, which my fellow-labourer, Mons. Hesse, took for a Trematode, and whose drawings had led me into error, lives like others at liberty while young, and soon fixes itself to a Clymenian, in order to pass as a messmate the later period of its life. We have called it

Cyclatella annelidicola, because of its residence in a Clymenian annelid. Claparède and Keferstein have observed a species, the Loxosoma singulare, on a capitellian annelid, of the genus Notomastus, at St. Vaast-la-Hogue, on the coast of Normandy. After this, Claparède found another species, the Loxosoma Kefersteinii, in the bay of Naples, on an Acamarchis, a bryozoarian mollusc. Mons. Kowalewsky has observed in the Bay of Naples the Loxosoma Napolitanum.

We found some years ago the Pedicellinæ in so great abundance in the oyster beds of Ostend, that the baskets and other things floating on the water were literally covered with them. We have several times since endeavoured to procure them again, but it was in vain to search in the same places where they were formerly so abundant: we have not been able to discover a single one.

The class of worms includes not only parasites, it contains also, as we shall see, true messmates; we find some on crustaceans, on molluscs, on animals of their own class, on Echinoderms, and on Polyps.

One of the most curious of these worms is the Myzostoma, whose true nature has just been revealed by the excellent researches of Mons. Mecznikow. These myzostomes resemble trematode worms, but they have symmetrical appendages, and are covered with vibratory ciliæ. They live on the comatulæ, and run upon these echinoderms with remarkable rapidity. They have not hitherto been found elsewhere; they are evidently no more parasites than the last mentioned, and their place is among free messmates. Two great annelids are found, the one, the Nereis bilineata, by the side of Paguri in the same shell, the other, the Nereis succinea, according

to Grube, in the tubes or galleries of the Teredines. These dangerous acolytes introduce themselves furtively into the retreat of their host; and, always on the watch, they obtain at all times, and in every place, a certain prey, and a hiding-place from which they can take their share of their neighbour’s goods. Another nereis, observed by Delle Chiaie, Nereis tethycola, lives in the cavities of a sponge, the Tethya pyrifera, which is visited by so many messmates and parasites, that it becomes a kind of hotel, where every one establishes himself at his ease. Risso also mentions a Lysidice erythrocephala which lives in sponges.

In the same class is found an Amphinoma, a beautiful red-blooded worm, which proudly wears a plume of red branchiæ on its head, and which Fritz Müller observed on the coast of Brazil, begging assistance from a poor Lepas anatifera. Many Polynoës live upon other annelids; the Harmothoë Malmgreni on the sheath of the Chœtopterus insignis, the Antinoe nobilis on the case of the Terebella nebulosa. Prof. Ray Lankester has lately communicated some observations on this subject to the Linnæan Society of London, and Dr. M’Intosh mentions some new species leading the same kind of life on the coast of Scotland.

Grube found at Trieste, in a star-fish (Astropecten aurantiacus), between its rows of suckers, a Polynoë malleata, with its stomach attached to the animal; and Delle Chiaie has lately observed on an asteria, a Nereis squamosa by the side of a Nereis flexuosa. Mons. Grube thinks that the nereis of Delle Chiaie is no other than the Polynoë malleata. Lobsters are often covered with very small tubicular worms, which invade the whole

carapace, and which, as true messmates, give themselves up to the caprices of their host. These are a kind of Spirorbis, which, under the form of small spiral tubes, instal themselves, by preference, on the limbs, the antennæ, or the claws.

Mr. A. Agassiz has seen on the coast of the United States, a Beroë (Mnemiopsis Leidyi) which gives lodging in its interior to worms which somewhat resemble the Hirudinidæ, and which doubtless live there as messmates. Mr. A. Agassiz has remarked to me another example of commensalism. On the coast of the territory of Washington, as far as California, is found a worm of the genus Lepidonotus, which always lives near the mouth of a star-fish, the Asteracanthion ochraceus of Brandt; sometimes as many as five are found together on a single individual, and are placed on different parts of the ambulacral rays. Mr. Pourtalis and Mr. Verril have observed annelids lodged in the polypidoms of the Stylaster.

There are few fish on which are not found Caligi, charming crustaceans which please the eye by their attenuated shape and their graceful movements. On these Caligi, which sometimes literally cover the skin of cod-fish coming from the north, we often find a curious trematode, the Udonella, which resembles one of the small hirudinidæ. Should this worm be placed among messmates? What is the part which it plays? We are persuaded that it is the same as that of the histriobdellæ under the tail of lobsters, that is to say, that it clears off the eggs of caligi which do not arrive at perfection, but perish in the course of their evolution.

Roussel de Vauzème has mentioned another worm, a

nematode, to which he has given the name of Odontobius, and which lives on the palatal membranes (the whalebones) of the southern whale. It is evidently a messmate. It can get nothing from the whalebones, but it snaps up on their passage in the interstices of the baleen, small animals of all kinds which swarm in these waters. When we open the Pylidium girans, we often find in the interior of its digestive cavity a larva, which was once thought to be descended from it, but instead of being allied to the Pylidium, this larva comes from a nemertian known by the name of Alardus caudatus. The young nemertian never abandons his host until it approaches the period of puberty, and then all the individuals living under the same conditions emancipate themselves at once, to pass the rest of their days free and roving like their mother.

Worms which have less freedom, like the Distomians, are sometimes both messmates and parasites. We find a remarkable example of this in the Distomum ocreatum of the Baltic. According to the observations of Willemoes-Suhm, this trematode passes its cercarial life freely in the sea, and instead of encysting itself in the body of a neighbour, it attaches itself to a copepod crustacean, the whole of the inside of which it devours, in order to clothe itself afterwards with the carapace of its victim. It is under the cover of its prey that it passes into the herring, and completes its sexual evolution.

Mons. Ulianin has recently found another Distome (Distomum ventricosum) which passes its cercarial life in freedom in the bay of Sebastopol, and completes its evolution in the fishes of the Black Sea. J. Müller has long since found Cercaria living freely in the Mediterranean.

We ourselves, some years ago, while making some researches among the Turbellaria, found among the eggs of some ordinary crabs of our coasts (Carcinus mænas), an interesting worm which we named Polia involuta, but which Prof. Kolliker appears to have known before, and designated by the name of Nemertes carcinophilus. It is not known whether it plays the same part as the Histriobdellæ and the Udonellæ. Delle Chiaie, as well as Prof. Frey and Prof. Leuckart, make mention of another nemertian which inhabits the Ascidia mamillata. Among the nemertians, we may allude to the Anoplodium parasita, which lives in the Holothuria tubulosa, and the Anoplodium Schneiderii, inhabiting the intestines of the Stichopus variegatus.

According to Mr. A. Agassiz, a species of Planarian (Planaria angulata, Mull.), lives as a free messmate on the lower surface of the Limulus, and prefers to establish itself near the base of the tail. Mons. Max Schultze recognized last year this same messmate on a limulus, which had died at Cologne in the large aquarium, and which had been sent to him for his anatomical studies. He showed at the congress of German naturalists at Wiesbaden, in 1873, the drawing which he had made of this animal, which he thought new to science. We may remark in passing, that he arrived, by means of his anatomical observations on Limuli, at the same result as did my son by his embryogenic observations, namely, that these supposed crustaceans are to be regarded as aquatic scorpions. Mr. Leidy also makes mention of Planarian parasites (Bdellura), with a sucker at the extremity of the body; and Mons. Giard noticed a blue one on the body of a Botryllus.

But of all the Turbellaria, the genus which appears to us the most interesting is the Temnophila, which Gay first observed on crabs at Chili, and which Professor Semper afterwards found on the crabs of the Philippine Islands. Gay and Phillipi found colonies of these animals on the body, the claws, and more especially the abdomen, of the Œglea. This messmate resembles a trematode by its form and by its posterior sucker, but by its entire character, and especially by its sexual organs, it belongs to the Turbellariæ. Mons. Blanchard calls it Temnophila Chilensis. Professor Semper saw at the Philippine Islands these Temnophilæ on river crabs, at five thousand feet above the level of the sea.

The Cydippe densa, a charming polyp of the Gulf of Naples, lodges in its gastro-vascular apparatus larvæ of annelids, which may as well be considered parasites as messmates. We owe to Panceri the first observations on these worms, of which two genera, Alciopina and Rhynconerulla, seem to live in the same manner in their youth. A naturalist, whose loss is profoundly deplored by the scientific world, Claparède, occupied himself with observations on these annelids during the last years of his life. It appears that these worms are so common in these polyps, that four have been found at once in the same animal.

The Spoon-worm, named by Œrsted, Sipunculus concharum, ought doubtless to find its place here. An oligochete worm, Hemidasys agaso, from the Gulf of Naples, lives on the Nereilepas caudata, and Claparède did not think it unworthy of his attention. The surest means of finding it, says this philosopher, is to look for it on this annelid; and our much regretted fellow-labourer

at Geneva did not abandon this messmate before he had completely studied it. Let us remark in passing, that Professor Grube published in 1831, at Königsberg, a special work on the abodes of annelids in general.

Cases of commensalism among the Echinodermata are still more rare. These animals are sufficiently provided with organs, both with respect to their food and their skin, not to require the assistance of their neighbours. We cannot rank as a phenomenon of commensalism, the conduct of the young Comatulæ, which fasten themselves, as Mr. A. Agassiz informs me, to the basal cirrhi of the adult echinoderms, and there form a little colony of young Pentacrinites.

We only know one Ophiurus (Ophiocnemis obscura), which lives as a messmate on a comatula, and consequently seeks assistance from an animal of its own rank. Another kind of Ophiuride (Asteromorpha lævis, Lym.) fixes itself on a Gorgonella Guadelupensis of Barbadoes. Everything induces us to suppose that we shall find more than one species of echinoderm, which will take its place among these when their mode of life has been studied with greater care. Professor Lütken has just proved this by quite recently making known another Ophiothela, which lives in the straits of Formosa, and seems to be the messmate of an Isidian polyp, known under the name of Parisis loxa. Another species (Oph. mirabilis) from Panama, infests certain Gorgoniæ and sponges; a third is found in the Fiji Islands on the Melitodes virgata; a fourth at the Isle of France on Gorgoniæ; and a fifth at Japan on the Mopsella Japonica. There is also another in the Pacific Ocean, but its companion is not known.

Professor Mobius, as well as Dr. F. Martens, has noticed a Hemicuryale pustulata on a polyp of Jamaica, known under the name of Verrucella Guadelupensis. This is a curious instance of mimicry.

The class of polyps includes several species which seek for assistance from others, and are classed among messmates. One of the most remarkable is the Gigantic Medusa, which can extend its arms downwards to a hundred and twenty feet, and bears the name of Cyanea arctica; the disc is seven feet and a half in diameter, and when the animal is on the surface of the water, the fringes, which surround the cavity at its mouth, occasionally afford lodging in the midst of them to a species of actinia, which lives there as messmate. Sometimes three, and even four or five, are found on a single Cyanæa. This also is an observation due to Mr. A. Agassiz, which he has published in his interesting work, “Sea-side Studies.” Prof. Haeckel supposed that the Geryoniæ produce Œginidæ by means of buds; but it appears that the learned professor was mistaken as to the nature of these buds; that instead of being produced one from the other, they have, according to Steenstrup, a completely different genealogy, being only united by conditions of good-fellowship. They may be truly called messmates.

Mons. Lacaze-Duthiers, who went to the coast of Africa to study corals, met with a young polyp which requires the assistance of another polyp in its early condition. This animal, to which he has given the name of Gerardia Lamarckii, lives on one of the Gorgoniæ, which it invades and stifles, as the lianas strangle the tree over which they spread themselves. But these same Gerardiæ can also

develop themselves on the eggs of the Plagiostoma, and are then capable of living separately. In the substance of this polyp lives a crustacean, the nature of which Mons. Lacaze-Duthiers has not yet made known.

The superb sponge, Euplectella aspergillum, the elegant structure of which cannot be sufficiently admired, is, unlike the Alcyonium of the Dromia, rooted to the soil, but nevertheless gives shelter to three kinds of crustaceans: Pinnotheres, Palemonidæ, and Isopods. These supposed plants have been known for many years under the Spanish name of Regadera, or the English “Venus’ Flower-basket;” they were first brought from Japan, and afterwards from the Moluccas, and more recently from the Philippine Islands. In almost all the individuals which Professor Semper was able to study in those parts, were found the same crustaceans. These Euplectellæ have just been met with to the south-west of Cape St. Vincent, by Wyville Thomson, who has brought up some from a depth of 1090 fathoms, while on board the Challenger. This skilful professor has discovered another sponge to the north-west of Scotland, at a depth of 460 fathoms; it bears the name of Holtenia Carpenteri; and I have in my possession a fine specimen which I owe to his generosity, and keep as a souvenir of the delightful hospitality which he extended to me at the Edinburgh meeting.

There are also sponges which construct a dwelling in the abode of their neighbour. We find, among others, a small sponge known under the name of Clione, which establishes itself in the substance of the shell of oysters, and hollows out galleries as the teredo does in wood.

Mr. Albany Hancock found twelve species of Clione on a single Tridacna. They are evidently not parasites, and I am not sure if their place is properly among messmates. The oyster, and more especially the Ostrea hippopus, lodges three or four different sorts in its shell. These Cliones possess siliceous spicules, by means of which they hollow out galleries in the substance of shells. Mr. Hancock has published a monograph of this genus, in which he recognizes twenty-four species collected from different shells, and two other species, which he refers to the genus Thoasa.

The cliones are real lodgers which lead us to the Saxicavæ, the Pholades, and the Teredines; they seek their lodging in rocks or in wood; these lead directly to the sea-urchins, which also hollow out lodgings in rocks, but without penetrating deeply. Professor Allman has just observed a very remarkable case of commensalism between a sponge and one of the tubulariæ. The crown of the tubularia is extended at the entrance of the canals of the sponge; and the association is so complete, that the Edinburgh professor imagined that he had before his eyes a true sponge with the arms of a tubularia.

In the lowest ranks of the animal scale, there are certain kinds of animalcules, which establish themselves on the bodies of obliging neighbours, and take advantage of their fins in order to swim at their expense. Thus we often find the bodies of certain crustaceans covered with a forest of vorticellæ and other infusoria. They cause themselves to be towed like cirrhipedes, but they do not change their toilet like them, so that it cannot be said that they put on the livery of servitude.

The kind of life led by several of these animalculæ is as yet little known.

Mons. Leydig has found in the stomach of the Hydatina Senta a messmate which much resembles an Euglena, and still more the Distigma tenax, Ehr.

[1] I owe this observation to Dr. W. S. Kent, who showed me, in London, anodonts attached in this manner to sticklebacks.

CHAPTER III.

FIXED MESSMATES.

The animals of which we have just spoken usually preserve their full and entire independence; from the time of their leaving the egg, till their complete development, they are subject to no other outward changes than such as belong to their class. If they sometimes renounce their liberty, it is only for a limited time; and they all preserve not only their peculiar appearance, but their organs intended for fishing or for locomotion. It is not thus with those which we are now about to consider; they are free in their youth, but as they draw near to puberty they make choice of a host, instal themselves within him, and completely lose their former appearance: not only do they throw aside their oars and their pincers, but they cease sometimes to keep up any communication with the outer world, and even give up the most precious organs of animal life, not even excepting those of the senses; they are installed for life, and their fate is bound up with the host which gives them shelter. The number of these messmates is considerable.

We shall first allude to some crustaceans named Cirrhipedes by Lamarck. The metamorphoses which they have undergone since they left the egg have so

much changed them, that Cuvier and all the zoologists of his age placed them in the class of mollusca. The incrustations of their skin resembled shells, which these creatures generally carry in the substance of their mantle.

These ambiguous creatures are far from being microscopic; there are Balani which attain the size of a walnut, and some have been found not less than ten inches high, as the Balanus psittacus. Some years since we saw on a piece of floating wood, found by fishermen in the North Sea, Anatifæ on the end of stalks from six to seven feet in length. The anatifæ themselves were of the usual size. These cirrhipedes belonged to every geological period; they have already been found in the Silurian formation, but, unlike the trilobites their contemporaries, they pass through all the ages, and, far from decreasing, they reign as masters at the present time in the two hemispheres.

It was an English naturalist, Thomson, who first made known the true nature of these singular organisms. So far were many from understanding their affinities with the other classes, that even after the excellent researches of the Belfast naturalist, they doubted their correctness, and supposed that these animals were allied both to the mollusca and to the articulata.

We see by this the immense progress which embryological studies have caused us to make in the appreciation of natural affinities. No one at the present time, who has seen a cirrhipede hatched, can retain any doubt as to the place which it ought to occupy. These crustaceans, taken as a whole, lead a life in which we find

more than one contrast; all live as wanderers when they first leave the egg, and they are hatched in such abundance on the coast, that the water becomes literally troubled with them. At the first period of their life, they have a supple and elegant body, and fins admirably divided, and the gracefulness of the postures which they assume does not yield in beauty to those of the most brilliant insect. After having spent some time in seeking adventures, they are seized with disgust for a nomad life; they choose a resting-place, and establish themselves by means of a cable which they afterwards abandon, and shelter themselves in an enclosed retreat for the rest of their days. Many cirrhipedes choose the back of a whale or the fin of a shark, and make the passage across the Atlantic or the Pacific in less time than the swiftest steamboats.

In many of these, recurrent development (I was about to say degradation) sometimes proceeds so far, that their animal nature becomes doubtful, and more than one of them, having no longer any mouth by which to feed, are reduced to a mere case which shelters their progeny. The messmate very nearly takes its rank among parasites. There are also cirrhipedes which live on different genera of their own family; and some species which are always found in society with other species. Some also live as messmates with each other; some of the Sabelliphili have one of the sexes parasitical on the other sex.

Crustaceans are usually diœcious; but because of their manner of life, the cirrhipedes sometimes unite the two sexes and thus render the preservation of the species more certain. The whole family of the Abdominalia, a name proposed by Darwin, if I am not mistaken, have

the sexes separate; and the males, comparatively very small, are attached to the body of each female. It is a case of polyandria which we see realized in the Scalpellum. Darwin made known the existence of supplementary males, so small and so little developed, that they are with difficulty discovered, and so badly are they provided with organs that they have neither those of motion nor a stomach to digest. We have not exhausted the strange peculiarities of this particular group; there are some which live without shells and claws in the inside of other cirrhipedes, and atrophied males which only exist at the expense of their own females.

It is almost useless to make the remark that more especially here there exist almost insensible gradations of difference between parasites, messmates, and free animals, and we shall find more than one example of this in the crustaceans to which we now allude.

The most interesting fixed messmates are evidently those cirrhipedes, which, under the name of Tubicinella, Diadema, or Coronula, cover the skins of whales. They are, like all the rest, free in their infancy, but soon they take shelter on the back or on the head of one of these huge cetaceans, which they never quit when they have once chosen their abode. That which gives them great importance is, that each whale lodges a particular species; so that the crustacean messmate is a true flag which indicates in some respect the nationality, and it would not be without interest for voyagers who are naturalists to study these living flags.

The great whale of the north, the Mysticetus, which our northern neighbours discovered while seeking for an eastern passage to India, a species which never leaves

the ice, carries no cirrhipedes. This fact was already known to Iceland fishermen of the twelfth century. The intrepid whalers of these regions used to distinguish a northern whale, without “calcareous plates,” from a southern whale with plates, that is to say, with cirrhipedes. This latter whale is the celebrated species of temperate regions, the Nord-Kaper which the Basques used to hunt, from the sixth century, in the Channel, and which they used afterwards to pursue even to Newfoundland. The whales of the southern hemisphere, like those of the Pacific Ocean, all have their own species of cirrhipedes. We found in the museum of the Zoological Garden at Amsterdam, a Coronula, brought from Japan by Mr. Blomhof, known under the name of Coronulæ reginæ, which, no doubt, characterizes the whale of those latitudes. Another northern whale, the Keporkak of the Greenlanders, very remarkable for its long fins, which give it the name of Megaptera, is covered very early in its life with these crustaceans, so much so, that the Greenlanders imagine that they are born with them. Some even have pretended to have seen Megapteræ covered with these coronulæ before their birth. Eschricht has in vain offered a reward to him who would send him coronulæ still attached to the umbilical cord; he has only received some pieces of skin covered with hairy bulbs. There is no doubt that young whales have been seen and captured while following their mother, which were already covered by these crustaceans.

Steenstrup has indicated the presence of Platycyamus Thompsoni on the body of the Hyperoodons, and the Xenobalanus globicipitis on the globiceps of the Shetland Isles.

The Cryptolepas is a new genus of Coronulidæ which

inhabits the coast of California, on the singular mysticete recently distinguished by the name of Rhachianectes glaucus. The Platylepas bisexlobata has lately been observed on one of the Sirenia, the Manatus latirostris. The marine turtles are also invaded by these singular animals, and their peculiar form, joined to their habitat, has given them the name of Chelonobia. It is not uncommon to find by the side of these Chelonobiæ, and even upon them, the Tanaïs, Serpulæ, and Bryozoariæ, forming together an animal forest on the cuirass of the turtle. The Matamata, a turtle living in the brackish water of Guiana, is covered with a cirrhipede more allied to the ordinary balani than to the chelonobiæ. Other living reptiles are not more exempt from cirrhipedes than turtles; the Dichelaspis pellucida and the Conchoderma Hunteri invade different sea-snakes. Many sharks harbour particular kinds, among which we mention the Alepas of the Spinax niger from the coasts of Norway. The same Alepas has been found on the Squalus glacialis at the same time as the Anelasma squalicola. Half a dozen varieties of these are known, one of which inhabits an echinoderm, another a decapod crustacean. These kinds of alepas are so reduced when they are adult, and are so completely despoiled of their distinctive attributes, that it is necessary to study them with especial care in their first dress, in order to recognize their parentage.

Other cirrhipedes establish themselves on neighbours of their own class, and we also find crustaceans upon other crustaceans. A pretty genus lives near Cape Verd on the carapace of a large lobster, and spreads itself on the centre of the back like a bouquet of flowers. My son has procured some very fine specimens, an

account of which he will publish, together with the other materials which he has collected during his passage across the Atlantic. Mr. John Denis Macdonald found in abundance on the branchiæ of a crab in Australia, the Neptunus pelagicus, which he places between the Lepas and the Dichelaspis.

The most singular, if not the most interesting of all these cirrhipedes, are the Gallæ, which appear under the tail of crabs or the abdomen of paguri, and which zoologists designate under the names of Peltogaster or Sacculina. They are found in both hemispheres. The recurrent development is so complete, that we can no longer distinguish any organic apparatus unless it be that of reproduction, and the whole body is a mere case enclosing within its walls eggs and spermatozoids. We see them very frequently under the abdomen of the crabs of our coasts, or even on the segments of the bodies of paguri. Mons. A. Giard has lately studied these animals. It is during the coupling season, according to him, that the Peltogasters establish themselves upon the crabs. Professor Semper has brought back quite a collection of them from his voyage to the Philippine Islands, and has entrusted them to one of his pupils, Dr. Kussmann, for the purposes of study. We heard him with great interest, at the late Congress at Wiesbaden, explain with remarkable clearness the results of his learned and conscientious observations. We do not think that we shall be wrong in adding that, for a long time, we shall see nothing better or more complete on this subject. All those cirrhipedes which adhere by their head to the skin of their host, by means of filaments, are now designated by the name of Rhizocephala.

A curious opinion, quite recently expressed by a naturalist, Mons. Giard, and which is a sign of the times, is that the Peltogaster of the Pagurus has become a Sacculina on the crab; the host having been transformed, its acolyte has done the same thing under the same influence.

Professor Semper has also found among the Philippine Islands, isopod crustaceans living as messmates after the manner of the peltogasters. Two cirrhipedes of the family of Peltogaster, the Sylon Hippolytes and the Sylon Pandali, have been found by Mons. Sars under the abdomen of the Pandalus brevirostris.

There are cirrhipedes on the gasteropod molluscs. The Concholepas Peruviana, that beautiful shell which has long been considered a rarity in our collections, is frequented by the Cryptophiolus minutus, only a sixth of an inch in length. The Scalpella often inhabit the Sertulariæ and other polyps; Oxynasps, Creusiæ, Pyrgomæ, and Lithotryæ inhabit corals. Certain kinds of sponges are regularly invaded by the Acastæ of Leach, eight species of which are mentioned by Darwin. As we find elsewhere parasites on parasites, here also we find messmates on messmates; on the common anatifa we perceive other genera, and on the Diadema of the North Pacific, we almost always see Otions and Cineras. The Protolepas bivincta also, a fifth of an inch in length, lives as a messmate in the mouth of the Alepas cornuta; and the Elminius of Leach also inhabits other cirrhipedes. The Hemioniscus balani, which Goodsir had taken some years ago for the male of the Balanus, is a messmate on these cirrhipedes. Parasites also are found in messmates; the soldier-crab gives lodging to the sexual

Eustoma truncata in its interior. A macrourous crustacean which we ought to mention here, the Galathea spinirostris, Dana, frequents a comatula, the colour of which it assumes; it is the same without doubt with the Pisa Styx, which lives on a polyp known by the name of Melitœa ochracea.

If we pass from the crustaceans to the molluscs, we have to notice in the first place an elegant gasteropod, the Phyllirhoa bucephala, which carries on its head a singular appendage, the nature of which has only lately been known; J. Müller took it at first for a medusa, then he abandoned this opinion, when at length Mons. Krohn referred it definitively to the lower polyps; it differs from its congeners only by its form, its tentacular cirrhi, and its mode of life: it is the Mnestra parasites. There are a great number of acephalous molluscs, which we might mention as messmates, but we will only refer to the Crenellæ which are regularly found in the substance of sponges.

The Philomedusa Vogtii of Fr. Müller, which lives on the Halcampa Fultoni, undoubtedly deserves to be mentioned here as a fixed messmate. Many bryozoa spread themselves over marine animals, and often engage in a deadly struggle with their patron. But among all these bryozoa we must mention an animal very common on the sea-shore at Ostend, and which one would take for a dried leaf, the Flustra membranacea. On the surface of these imitative leaves are found little bouquets of other bryozoa, which are either Crisiæ or Scrupocellariæ. Another kind, which has also passed for a gelatinous plant, bears the name of Halodactylus. Without any microscopic study, one can obtain an idea of these colonies.

One of these Halodactyles spreads itself upon the stalk of a Sertularia, all the inhabitants of which it stifles, so that it is the victim himself who serves as a guardian to the invader.

These Halodactyli are very widely spread over the Northern Seas, and often establish themselves on the large horse-hoof oyster. Michelin has noticed under the name of parasite a fossil cellepore from the saltpits of Touraine and Anjou, which entirely surrounds the shell of a gasteropod; in order to prevent its patron from dying of hunger, the bryozoon develops itself around the mouth like a gallery, and prolongs its last spiral. This Cellepora parasitica has evidently a place here.

Many of these messmate bryozoa are found in a fossil state in the crag of the Antwerp basin.

We have still to mention among fixed messmates many polyps, some of which are very remarkable. Thus, many naturalists speak of vast colonies of polyps in which lodge various animals which shelter themselves there like paguri in deserted shells.

Among these are the colonies of which Forster speaks, which are not less than three feet in diameter, and fifteen feet in height, with a crown of eighteen feet in diameter. Dana also makes mention of an Astræa of twelve feet in height, and of Porites twenty feet high, which contain more than five millions of individuals, among which a number of animals come to take refuge.

The Museum of Natural History at Paris is in possession of a superb specimen of Porites conglomerata: in the middle of the colony lodges a Tridacna (Trid. corallicola, Val.) like a pagurus under a forest of hydractiniæ. This remarkable polyp was brought from

the Seychelles Islands by Mons. L. Rousseau. It is not impossible that pinnotheres live in this same tridacna, and that we have there a fresh example of messmate within messmate.

In the Bay of Massachusetts, on the coast of New England, another curious messmate lives at great depths; Dana has lately described it, under the name of Epizoanthus Americanus, V. It establishes itself in the Eupagurus pubescens. The Sertularia parasitica of the gulf of Naples, from which I have formed the genus Corydendrium, is a messmate after the manner of an infinite number of other polyps. In closing this list, we shall mention a polyp, named Halicondria suberea, and the Actinia carcinopodus of Otto, which inhabit an univalve mollusc; as also the Heterosammiæ and the Heterocyathi of the family of Turbinolidæ, which lodge in a trochoid shell.

The sponges, placed by naturalists by turns among plants or on the confines of the animal kingdom, are now generally regarded as polyps; this is the opinion expressed by Haeckel, who wishes at the same time to replace the term Cœlenterata by that of Zoophytes. The learned naturalist of Jena, when making this proposition, should have remembered that in 1859 we placed the sponges in the group of polyps, as the lowest in the scale; and that we proposed, from the time when the acalephæ were recognized to be adult polyps, to designate all these animals under the name of Polyps. Some time after, R. Leuckart proposed the appellation Cœlenterate Polyps, which has been generally received. Professor Haeckel would have lost nothing by acknowledging that in 1873 he arrived at a result similar to

that to which I had come twenty years before, and that it is not a very happy innovation to change the term polyps for zoophytes. It is the more surprising that this naturalist has forgotten to quote my opinion, since at the congress of naturalists at Hanover in 1866, I had placed this question on the agenda for an ordinary meeting.

I maintained, in opposition to the opinion of the naturalists whose authority had been especially recognized in the matter (Osc. Schmidt, who was present, among others), that sponges are lower polyps, whether they are regarded as to their development or their organization.

This group, so remarkable in form, so varied in colour and appearance, very often affords examples of animals which live with them as true messmates; and we find the same relations established between them in both hemispheres. As we observe rhizophales on crabs and soldier-crabs, and pinnotheres on bivalve molluscs, so we find that the sponges of the Indian Seas or of Japan harbour the same messmates which we discover on them in the Northern Seas or the Atlantic.

In the sea of Japan is found a very remarkable sponge, generally known by the name of Hyalonema. It is a bundle of spicules like threads of glass, which seem artificially tied together, and on the surface of which we regularly find a polyp of the genus Polythoa. The nature of this sponge, and its relations with the polyps which surround it, have been discussed for many years. Ehrenberg had recognized the polyp Polythoa around the spicules, but the Hyalonema was considered by him as an artificial product. The Polythoæ were regarded as only a case in which had been placed this

bundle of spicules. The learned microscopist of Berlin had even thought that he had found the proof of this opinion in the presence of woollen threads which were observed in a specimen which Mons. Barbosa du Bocage had sent him from Lisbon. Woollen threads had indeed adhered to the spicules of Hyalonema, but they came from the fishermen, who, when they drew these sponges from the water, placed them carefully in their bosoms under their woollen jerseys.

Dr. Gray, of the British Museum, considers the sponge as a parasite of the Polythoa, and that the bundle of spicules belongs, not to the sponge, but to the polyp. The most learned naturalist on the subject of sponges, Mr. Bowerbank, expresses a different opinion. The sponge and its spicules, according to him, are but a single body, and the polyps are only a part of it. The supposed polyps would only form a cloacal system for the use of the sponge colony.

Valenciennes, guided no doubt by the observations of Philippe Poteau, was the first to recognise the nature of the sponge and its spicules, but it is to Max Schultze that we must give the credit of distinguishing the true character of this extraordinary marine production. He has shown that the bundle is formed by the extraordinarily long spicules of the sponge, and that the polyp establishes itself upon it, by forming a sheath around the bundle.