The Cambridge natural history, Vol. 05 (of 10)

THE

CAMBRIDGE NATURAL HISTORY

EDITED BY

S. F. HARMER, M.A., Fellow of King's College, Cambridge; Superintendent of the University Museum of Zoology

AND

A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge; University Lecturer on the Morphology of Invertebrates

VOLUME V

PERIPATUS

By Adam Sedgwick, M.A., F.R.S., Fellow and Lecturer of Trinity College, Cambridge

MYRIAPODS

By F. G. Sinclair, M.A., Trinity College, Cambridge

INSECTS

PART I. Introduction, Aptera, Orthoptera, Neuroptera, and a portion of Hymenoptera (Sessiliventres and Parasitica)

By David Sharp, M.A. (Cantab.), M.B. (Edinb.), F.R.S.

London
MACMILLAN AND CO.
AND NEW YORK
1895

All rights reserved

"Creavit in cœlo Angelos, in terra vermiculos: non superior in illis, non inferior in istis. Sicut enim nulla manus Angelum, ita nulla posset creare vermiculum."—Saint Augustine, Liber soliloquiorum animae ad Deum, Caput IX.

CONTENTS

SCHEME OF THE CLASSIFICATION (RECENT FORMS) ADOPTED IN THIS BOOK

MYRIAPODA
Order.		Family.
CHILOGNATHA (= DIPLOPODA)		Polyxenidae (p. [43]). Glomeridae (p. [43]). Sphaerotheriidae (p. [43]). Julidae (p. [43]). Blanjulidae (p. [44]). Chordeumidae (p. [44]). Polydesmidae (p. [44]). Polyzoniidae (p. [44]).
CHILOPODA		Lithobiidae (p. [45]). Scolopendridae (p. [45]). Notophilidae (p. [45]). Geophilidae (p. [46]).
SCHIZOTARSIA		Cermatiidae (= Scutigeridae) (p. [46]).
SYMPHYLA.		Scolopendrellidae (p. [46]).
PAUROPODA		Pauropidae (p. [47]).

INSECTA
Order.		Division, Series, or Sub-Order.		Family.		Tribe or Sub-Family.		Group.
APTERA (p. [180])		Thysanura (p. [182])		Campodeidae (p. [183]). Japygidae (p. [184]). Machilidae (p. [184]). Lepismidae (p. [185]).
		Collembola (p. [189])		Lipuridae (p. [190]). Poduridae (p. [190]). Smynthuridae (p. [191]).
ORTHOPTERA (p. [198])		Orthoptera cursoria		Forficulidae (p. [202]). Hemimeridae (p. [217]).
				Blattidae (p. [220])		Ectobiides. Phyllodromiides. Nyctiborides. Epilamprides. Periplanetides. Panchlorides. Blaberides. Corydiides. Oxyhaloides. Perisphaeriides. Panesthiides. ? Geoscapheusides.
				Mantidae (p. [242])		Amorphoscelides. Orthoderides. Mantides. Harpagides. Vatides. Empusides.
				Phasmidae (p. [260])		Lonchodides. Bacunculides. Bacteriides. Necroscides. Clitumnides. Acrophyllides. Cladomorphides. Anisomorphides. Phasmides. Aschipasmides. Bacillides. Phylliides.
		Orthoptera saltatoria		Acridiidae (p. [279])		Tettigides. Pneumorides. Mastacides. Proscopiides. Tryxalides. Oedipodides. Pyrgomorphides. Pamphagides. Acridiides.
				Locustidae (p. [311])		Phaneropterides. Meconemides. Mecopodides. Prochilides. Pseudophyllides. Conocephalides. Tympanophorides. Sagides. Locustides. Decticides. Callimenides. Ephippigerides. Hetrodides. Gryllacrides. Stenopelmatides.
				Gryllidae (p. [330])		Tridactylides. Gryllotalpides. Myrmecophilides. Gryllides. Oecanthides. Trigonidiides. Eneopterides.
NEUROPTERA (p. [341])		Mallophaga (p. [345])				Leiotheides. Philopterides.
		Pseudoneuroptera		Embiidae (p. [351]). Termitidae (p. [356]). Psocidae (p. [390]).
		Neuroptera Amphibiotica		Perlidae (p. [398]).
				Odonata (p. [409])		Anisopterides		Gomphinae. Cordulegasterinae. Aeschninae. Corduliinae. Libellulinae.
						Zygopterides		Calepteryginae. Agrioninae.
				Ephemeridae (p. [429]).
		Neuroptera planipennia		Sialidae (p. [444])		Sialides. Raphidiides.
				Panorpidae (p. [449]).
				Hemerobiidae (p. [453])		Myrmeleonides (p. [454]).
						Ascalaphides (p. [459])		Holophthalmi. Schizophthalmi.
						Nemopterides (p. [462]). Mantispides (p. [463]).
						Hemerobiides (p. [465])		Dilarina. Nymphidina. Osmylina. Hemerobiina.
						Chrysopides (p. [469]). Coniopterygides (p. [471]).
		Trichoptera		Phryganeidae (p. [473])		Phryganeides (p. [480]). Limnophilides (p. [481]). Sericostomatides (p. [482]). Leptocerides (p. [482]). Hydropsychides (p. [482]). Rhyacophilides (p. [483]). Hydroptilides (p. [484]).
HYMENOPTERA (p. [487])		Hymenoptera Sessiliventres		Cephidae (p. [504]). Oryssidae (p. [506]). Siricidae (p. [507]). Tenthredinidae (p. [510]).
		Hymenoptera Petiolata (part)		Cynipidae (p. [523]). Proctotrypidae (p. [533]). Chalcididae (p. [539]). Ichneumonidae (p. [551]). Braconidae (p. [558]). Stephanidae (p. [561]). Megalyridae (p. [562]). Evaniidae (p. [562]). Pelecinidae (p. [563]). Trigonalidae (p. [564]).
(To be continued in Vol. VI.)

PERIPATUS

BY

ADAM SEDGWICK, M.A., F.R.S.

Fellow of Trinity College, Cambridge.

CHAPTER I

PERIPATUS

INTRODUCTION–EXTERNAL FEATURES–HABITS–BREEDING–ANATOMY–ALIMENTARY CANAL–NERVOUS SYSTEM–THE BODY WALL–THE TRACHEAL SYSTEM–THE MUSCULAR SYSTEM–THE VASCULAR SYSTEM–THE BODY CAVITY–NEPHRIDIA–GENERATIVE ORGANS–DEVELOPMENT–SYNOPSIS OF THE SPECIES–SUMMARY OF DISTRIBUTION.

The genus Peripatus was established in 1826 by Guilding,[^[1]] who first obtained specimens of it from St. Vincent in the Antilles. He regarded it as a Mollusc, being no doubt deceived by the slug-like appearance given by the antennae. Specimens were subsequently obtained from other parts of the Neotropical region and from South Africa and Australia, and the animal was variously assigned by the zoologists of the day to the Annelida and Myriapoda. Its true place in the system, as a primitive member of the group Arthropoda, was first established in 1874 by Moseley,[^[2]] who discovered the tracheae. The genus has been monographed by Sedgwick,[^[3]] who has also written an account of the development of the Cape species.[^[4]] A bibliography will be found in Sedgwick's Monograph.

There can be no doubt that Peripatus is an Arthropod, for it possesses the following features, all characteristic of that group, and all of first-class morphological importance: (1) The presence of appendages modified as jaws; (2) the presence of paired lateral ostia perforating the wall of the heart and putting its cavity in communication with the pericardium; (3) the presence of a vascular body cavity and pericardium (haemocoelic body cavity); (4) absence of a perivisceral section of the coelom. Finally, the tracheae, though not characteristic of all the classes of the Arthropoda, are found nowhere outside that group, and constitute a very important additional reason for uniting Peripatus with it.

Peripatus, though indubitably an Arthropod, differs in such important respects from all the old-established Arthropod classes, that a special class, equivalent in rank to the others, and called Prototracheata, has had to be created for its sole occupancy. This unlikeness to other Arthropoda is mainly due to the Annelidan affinities which it presents, but in part to the presence of the following peculiar features: (1) The number and diffusion of the tracheal apertures; (2) the restriction of the jaws to a single pair; (3) the disposition of the generative organs; (4) the texture of the skin; and (5) the simplicity and similarity of all the segments of the body behind the head.

The Annelidan affinities are superficially indicated in so marked a manner by the thinness of the cuticle, the dermo-muscular body wall, the hollow appendages, that, as already stated, many of the earlier zoologists who examined Peripatus placed it amongst the segmented worms; and the discovery that there is some solid morphological basis for this determination constitutes one of the most interesting points of the recent work on the genus. The Annelidan features are: (1) The paired nephridia in every segment of the body behind the first two (Saenger, Balfour[^[5]]); (2) the presence of cilia in the generative tracts (Gaffron). It is true that neither of these features are absolutely distinctive of the Annelida, but when taken in conjunction with the Annelidan disposition of the chief systems of organs, viz. the central nervous system, and the main vascular trunk or heart, may be considered as indicating affinities in that direction. Peripatus, therefore, is zoologically of extreme interest from the fact that, though in the main Arthropodan, it possesses features which are possessed by no other Arthropod, and which connect it to the group to which the Arthropoda are in the general plan of their organisation most closely related. It must, therefore, according to our present lights, be regarded as a very primitive form; and this view of it is borne out by its extreme isolation at the present day. Peripatus stands absolutely alone as a kind of half-way animal between the Arthropoda and Annelida. There is no gradation of structure within the genus; the species are very limited in number, and in all of them the peculiar features above mentioned are equally sharply marked.

Peripatus, though a lowly organised animal, and of remarkable sluggishness, with but slight development of the higher organs of sense, with eyes the only function of which is to enable it to avoid the light—though related to those animals most repulsive to the aesthetic sense of man, animals which crawl upon their bellies and spit at, or poison, their prey—is yet, strange to say, an animal of striking beauty. The exquisite sensitiveness and constantly changing form of the antennae, the well-rounded plump body, the eyes set like small diamonds on the side of the head, the delicate feet, and, above all, the rich colouring and velvety texture of the skin, all combine to give these animals an aspect of quite exceptional beauty. Of all the species which I have seen alive, the most beautiful are the dark green individuals of Capensis, and the species which I have called Balfouri. These animals, so far as skin is concerned, are not surpassed in the animal kingdom. I shall never forget my astonishment and delight when on bearing away the bark of a rotten tree-stump in the forest on Table Mountain, I first came upon one of these animals in its natural haunts, or when Mr. Trimen showed me in confinement at the South African Museum a fine fat, full-grown female, accompanied by her large family of thirty or more just-born but pretty young, some of which were luxuriously creeping about on the beautiful skin of their mother's back.

External Features.

The anterior part of the body may be called the head, though it is not sharply marked off from the rest of the body (Fig. 1).

Fig. 1.—Peripatus capensis, drawn from life. Life size. (After Sedgwick.)

Fig. 2.—Ventral view of hind-end of P. Novae-Zealandiae. (After Sedgwick.) g, Generative opening; a, anus.

Fig. 3.—Ventral view of the head of P. capensis. (After Sedgwick.) ant, Antennae; or.p, oral papillae; F.1, first leg; T, tongue.

The head carries three pairs of appendages, a pair of simple eyes, and a ventrally placed mouth. The body is elongated and vermiform; it bears a number of paired appendages, each terminating in a pair of claws, and all exactly alike. The number varies in the different species. The anus is always at the posterior end of the body, and the generative opening is on the ventral surface just in front of the anus; it may be between the legs of the last pair (Fig. 2), or it may be behind them. There is in most species a thin median white line extending the whole length of the dorsal surface of the body, on each side of which the skin pigment is darker than elsewhere. The colour varies considerably in the different species, and even in different individuals of the same species. The ventral surface is nearly always flesh-coloured, while the dorsal surface has a darker colour. In the South African species the colour of the dorsal surface varies from a dark green graduating to a bluish gray, to a brown varying to a red orange. The colour of the Australasian species varies in like manner, while that of the Neotropical species (S. American and W. Indian) is less variable. The skin is thrown into a number of transverse ridges, along which wart-like papillae are placed. The papillae, which are found everywhere, are specially developed on the dorsal surface, less so on the ventral. Each papilla carries at its extremity a well-marked spine.

The appendages of the head are the antennae, the jaws and the oral papillae.

The antennae, which are prolongations of the dorso-lateral parts of the head, are ringed, and taper slightly till near their termination, where they are slightly enlarged. The rings bear a number of spines, and the free end of the antennae is covered by a cap of spiniferous tissue like that of the rings.

Fig. 4.—Inner jaw-claw of P. capensis. (After Balfour.)

Fig. 5.—Outer jaw-claw of P. capensis. (After Balfour.)

The mouth is at the hinder end of a depression called the buccal cavity, and is surrounded by an annular tumid lip, raised into papilliform ridges and bearing a few spines (Fig. 3). Within the buccal cavity are the two jaws. They are short, stump-like, muscular structures, armed at their free extremities by a pair of cutting blades or claws, and are placed one on each side of the mouth. In the median line of the buccal cavity in front is placed a thick muscular protuberance, which may be called the tongue, though attached to the dorsal instead of to the ventral wall of the mouth (Fig. 3). The tongue bears a row of small chitinous teeth. The jaw-claws (Figs. 4 and 5), which resemble in all essential points the claws borne by the feet, and like these are thickenings of the cuticle, are sickle-shaped. They have their convex edge directed forwards and their concave or cutting edge turned backwards. The inner cutting plate (Fig. 4) usually bears a number of cutting teeth. The jaws appear to be used for tearing the food, to which the mouth adheres by means of the tumid suctorial lips. The oral papillae are placed at the sides of the head (Fig. 3). The ducts of the slime-glands open at their free end. They possess two main rings of projecting tissue, and their extremities bear papillae irregularly arranged.

The ambulatory appendages vary in number. There are seventeen pairs in P. capensis and eighteen in P. Balfouri, while in P. Edwardsii the number varies from twenty-nine to thirty-four pairs. They consist of two main divisions, which we may call the leg and the foot (Figs. 6 and 7). The leg (l) has the form of a truncated cone, the broad end of which is attached to the ventro-lateral wall of the body, of which it is a prolongation. It is marked by a number of rings of papillae placed transversely to its long axis, the dorsal of which are pigmented like the dorsal surface of the body, and the ventral like the ventral surface. At the narrow distal end of the leg there are on the ventral surface three spiniferous pads, each of which is continued dorsally into a row of papillae.

Fig. 6.—Ventral view of last leg of a male P. capensis. (After Sedgwick.) f, Foot; l, leg; p, spiniferous pads. The white papilla on the proximal part of this leg is characteristic of the male of this species.

Fig. 7.—Leg of P. capensis seen from the front. (After Sedgwick.) f, Foot; l, leg; p, spiniferous pads.

The foot is attached to the distal end of the leg. It is slightly narrower at its attached extremity than at its free end. It bears two sickle-shaped claws and a few papillae. The part of the foot which carries the claws is especially retractile, and is generally found more or less telescoped into the proximal part. The legs of the fourth and fifth pairs differ from the others in the fact that the proximal pad is broken up into three, a small central and two larger lateral. The enlarged nephridia of these legs open on the small central division.

The males are generally rather smaller than the females. In those species in which the number of legs varies, the male has a smaller number of legs than the female.

Habits.

They live beneath the bark of rotten stumps of trees, in the crevices of rock, and beneath stones. They require a moist atmosphere, and are exceedingly susceptible to drought. They avoid light, and are therefore rarely seen. They move with great deliberation, picking their course by means of their antennae and eyes. It is by the former that they acquire a knowledge of the ground over which they are travelling, and by the latter that they avoid the light. The antennae are extraordinarily sensitive, and so delicate, indeed, that they seem to be able to perceive the nature of objects without actual contact. When irritated they eject with considerable force the contents of their slime reservoirs from the oral papillae. The force is supplied by the sudden contraction of the muscular body wall. They can squirt the slime to the distance of almost a foot. The slime, which appears to be perfectly harmless, is extremely sticky, but it easily comes away from the skin of the animal itself.

I have never seen them use this apparatus for the capture of prey, but Hutton describes the New Zealand species as using it for this purpose. So far as I can judge, it is used as a defensive weapon; but this of course will not exclude its offensive use. They will turn their heads to any part of the body which is being irritated and violently discharge their slime at the offending object. Locomotion is effected entirely by means of the legs, with the body fully extended.

Of their food in the natural state we know little; but it is probably mainly, if not entirely, animal. Hutton describes his specimens as sucking the juices of flies which they had stuck down with their slime, and those which I kept in captivity eagerly devoured the entrails of their fellows, and the developing young from the uterus. They also like raw sheep's liver. They move their mouths in a suctorial manner, tearing the food with their jaws. They have the power of extruding their jaws from the mouth, and of working them alternately backwards or forwards. This is readily observed in individuals immersed in water.

Breeding.

All species are viviparous. It has been lately stated that one of the Australian species is normally oviparous, but this has not been proved. The Australasian species come nearest to laying eggs, inasmuch as the eggs are large, full of yolk, and enclosed in a shell; but development normally takes place in the uterus, though, abnormally, incompletely developed eggs are extruded.

The young of P. capensis are born in April and May. They are almost colourless at birth, excepting the antennae, which are green, and their length is 10 to 15 mm. A large female will produce thirty to forty young in one year. The period of gestation is thirteen months, that is to say, the ova pass into the oviducts about one month before the young of the preceding year are born. They are born one by one, and it takes some time for a female to get rid of her whole stock of embryos; in fact, the embryos in any given female differ slightly in age, those next the oviduct being a little older (a few hours) than those next the vagina. The mother does not appear to pay any special attention to her young, which wander away and get their own food.

There does not appear to be any true copulation. The male deposits small, white, oval spermatophores, which consist of small bundles of spermatozoa cemented together by some glutinous substance, indiscriminately on any part of the body of the female. Such spermatophores are found on the bodies of both males and females from July to January, but they appear to be most numerous in our autumn. It seems probable that the spermatozoa make their way from the adherent spermatophore through the body wall into the body, and so by traversing the tissues reach the ovary. The testes are active from June to the following March. From March to June the vesiculae of the male are empty.

There are no other sexual differences except in some of the South African species, in which the last or penultimate leg of the male bears a small white papilla on its ventral surface (Fig. 6).

Whereas in the Cape species embryos in the same uterus are all practically of the same age (except in the month of April, when two broods overlap in P. capensis), and birth takes place at a fixed season; in the Neotropical species the uterus, which is always pregnant, contains embryos of different ages, and births probably take place all the year round.

In all species of Peripatus the young are fully formed at birth, and differ from the adults only in size and colour.

ANATOMY

The Alimentary Canal (Fig. 8).

Fig. 8.—Peripatus capensis dissected so as to show the alimentary canal, slime glands, and salivary glands. (After Balfour.) The dissection is viewed from the ventral side, and the lips (L) have been cut through in the middle line behind and pulled outwards so as to expose the jaws (j), which have been turned outwards, and the tongue (T) bearing a median row of chitinous teeth, which branches behind into two. The muscular pharynx, extending back into the space between the first and second pairs of legs, is followed by a short tubular oesophagus. The latter opens into the large stomach with plicated walls, extending almost to the hind end of the animal. The stomach at its point of junction with the rectum presents an S-shaped ventro-dorsal curve. A, Anus; at, antenna; F.1, F.2, first and second feet; j, jaws; L, lips; oe, oesophagus; or.p, oral papilla; ph, pharynx; R, rectum; s.d, salivary duct; s.g, salivary gland; sl.d, slime reservoir; sl.g, portion of tubules of slime gland; st, stomach; T, tongue in roof of mouth.

The buccal cavity, as explained above, is a secondary formation around the true mouth, which is at its dorsal posterior end. It contains the tongue and the jaws, which have already been described, and into the hind end of it there opens ventrally by a median opening the salivary glands (s.g). The mouth leads into a muscular pharynx (ph), which is connected by a short oesophagus (oe) with a stomach (st). The stomach forms by far the largest part of the alimentary canal. It is a dilated soft-walled tube, and leads behind into the short narrow rectum (R), which opens at the anus. There are no glands opening into the alimentary canal.

Nervous System.

The central nervous system consists of a pair of supra-oesophageal ganglia united in the middle line, and of a pair of widely divaricated ventral cords, continuous in front with the supra-oesophageal ganglia (Fig. 9).

The ventral cords at first sight appear to be without ganglionic thickenings, but on more careful examination they are found to be enlarged at each pair of legs (Fig. 9). These enlargements may be regarded as imperfect ganglia. There are, therefore, as many pairs of ganglia as there are pairs of legs. There is in addition a ganglionic enlargement at the commencement of the oesophageal commissures, where the nerves to the oral papillae are given off (Fig. 9, or.g).

Fig. 9.—Brain and anterior part of the ventral nerve-cords of Peripatus capensis enlarged and viewed from the ventral surface. (After Balfour.) The paired appendages (d) of the ventral surface of the brain are seen, and the pair of sympathetic nerves (sy) arising from the ventral surface of the hinder part. From the commencement of the oesophageal commissures pass off on each side a pair of nerves to the jaws (Jn). The three anterior commissures between the ventral nerve-cords are placed close together; immediately behind them the nerve-cords are swollen, to form the ganglionic enlargements from which pass off to the oral papillae a pair of large nerves on each side (orn). Behind this the cords present a series of enlargements, one pair for each pair of feet, from which a pair of large nerves pass off on each side to the feet (pn). atn, Antennary nerves; co, commissures between ventral cords; d, ventral appendages of brain; E, eye; en, nerves passing outwards from ventral cord; F.g.1, ganglionic enlargements from which nerves to feet pass off; jn, nerves to jaws; org, ganglionic enlargement from which nerves to oral papillae pass off; orn, nerves to oral papillae; pc, posterior lobe of brain; pn, nerves to feet; sy, sympathetic nerves.

The ventral cords are placed each in the lateral compartments of the body cavity, immediately within the longitudinal layer of muscles. They are connected with each other, rather like the pedal nerves of Chiton and the lower Prosobranchiata, by a number of commissures. These commissures exhibit a fairly regular arrangement from the region included between the first and the last pair of true feet. There are nine or ten of them between each pair of feet. They pass along the ventral wall of the body, perforating the ventral mass of longitudinal muscles. On their way they give off nerves which innervate the skin.

Posteriorly the two nerve-cords nearly meet immediately in front of the generative aperture, and then, bending upwards, fall into each other dorsally to the rectum. They give off a series of nerves from their outer borders, which present throughout the trunk a fairly regular arrangement. From each ganglion two large nerves (pn) are given off, which, diverging somewhat from each other, pass into the feet.

From the oesophageal commissures, close to their junction with the supra-oesophageal ganglia, a nerve arises on each side which passes to the jaws, and a little in front of this, apparently from the supra-oesophageal ganglion itself, a second nerve to the jaws also takes its origin.

The supra-oesophageal ganglia (Fig. 9) are large, somewhat oval masses, broader in front than behind, completely fused in the middle, but free at their extremities. Each of them is prolonged anteriorly into an antennary nerve, and is continuous behind with one of the oesophageal commissures. On the ventral surface of each, rather behind the level of the eye, is placed a hollow protuberance (Fig. 9, d), of which I shall say more in dealing with the development. About one-third of the way back the two large optic nerves take their origin, arising laterally, but rather from the dorsal surface (Fig. 9). Each of them joins a large ganglionic mass placed immediately behind the retina.

The histology of the ventral cords and oesophageal commissures is very simple and uniform. They consist of a cord almost wholly formed of nerve-fibres placed dorsally, and of a ventral layer of ganglion cells.

The Body Wall.

The skin is formed of three layers.

(1) The cuticle.

(2) The epidermis or hypodermis.

(3) The dermis.

The cuticle is a thin layer. The spines, jaws, and claws are special developments of it. Its surface is not, however, smooth, but is everywhere, with the exception of the perioral region, raised into minute secondary papillae, which in most instances bear at their free extremity a somewhat prominent spine. The whole surface of each of the secondary papillae just described is in its turn covered by numerous minute spinous tubercles.

The epidermis, placed immediately within the cuticle, is composed of a single layer of cells, which vary, however, a good deal in size in different regions of the body. The cells excrete the cuticle, and they stand in a very remarkable relation to the secondary papillae of the cuticle just described. Each epidermis cell is in fact placed within one of these secondary papillae, so that the cuticle of each secondary papilla is the product of a single epidermis cell. The pigment which gives the characteristic colour to the skin is deposited in the protoplasm of the outer ends of the cells in the form of small granules.

At the apex of most, if not all, the primary wart-like papillae there are present oval aggregations, or masses of epidermis cells, each such mass being enclosed in a thickish capsule and bearing a long projecting spine. These structures are probably tactile organs. In certain regions of the body they are extremely numerous; more especially is this the case in the antennae, lips, and oral papillae. On the ventral surface of the peripheral rings of the thicker sections of the feet they are also very thickly set and fused together so as to form a kind of pad (Figs. 6 and 7). In the antennae they are thickly set side by side on the rings of skin which give such an Arthropodan appearance to these organs in Peripatus.

The Tracheal System.

The apertures of the tracheal system are placed in the depressions between the papillae or ridges of the skin. Each of them leads into a tube, which may be called the tracheal pit (Fig. 10), the walls of which are formed of epithelial cells bounded towards the lumen of the pit by a very delicate cuticular membrane continuous with the cuticle covering the surface of the body. The pits vary somewhat in depth; the pit figured was about 0.09 mm. It perforates the dermis and terminates in the subjacent muscular layer.

Internally it expands in the transverse plane and from the expanded portion the tracheal tubes arise in diverging bundles. Nuclei similar in character to those in the walls of the tracheal pit are placed between the tracheae, and similar but slightly more elongated nuclei are found along the bundles. The tracheae are minute tubes exhibiting a faint transverse striation which is probably the indication of a spiral fibre. They appear to branch, but only exceptionally. The tracheal apertures are diffused over the surface of the body, but are especially developed in certain regions.

Fig. 10.—Section through a tracheal pit and diverging bundles of tracheal tubes taken transversely to the long axis of the body. (After Balfour.) tr, Tracheae, showing rudimentary spiral fibre; tr.c, cells resembling those lining the tracheal pits, which occur at intervals along the course of the tracheae; tr.o, tracheal stigma; tr.p, tracheal pit.

The Muscular System.

The general muscular system consists of—(1) the general wall of the body; (2) the muscles connected with the mouth, pharynx, and jaws; (3) the muscles of the feet; (4) the muscles of the alimentary tract.

The muscular wall of the body is formed of—(1) an external layer of circular fibres; (2) an internal layer of longitudinal muscles.

The main muscles of the body are unstriated and divided into fibres, each invested by a delicate membrane. The muscles of the jaws alone are transversely striated.

The Vascular System.

The vascular system consists of a dorsal tubular heart with paired ostia leading into it from the pericardium, of the pericardium, and the various other divisions of the perivisceral cavity (Fig. 14, D). As in all Arthropoda, the perivisceral cavity is a haemocoele; i.e. it contains blood and forms part of the vascular system. The heart extends from close to the hind end of the body to the head.

The Body Cavity.

The body cavity is formed of four compartments—one central, two lateral, and a pericardial (Fig. 14, D). The former is by far the largest, and contains the alimentary tract, the generative organs, and the slime glands. It is lined by a delicate endothelial layer, and is not divided into compartments nor traversed by muscular fibres. The lateral divisions are much smaller than the central, and are shut off from it by the inner transverse band of muscles. They are almost entirely filled with the nerve-cord and salivary gland in front and with the nerve-cord alone behind, and their lumen is broken up by muscular bands. They further contain the nephridia. They are prolonged into the feet, as is the embryonic body cavity of most Arthropoda. The pericardium contains a peculiar cellular tissue, probably, as suggested by Moseley, equivalent to the fat-bodies of insects.

Nephridia.

In Peripatus capensis nephridia are present in all the legs. In all of them (except the first three) the following parts may be recognised (Fig. 11):—

(1) A vesicular portion opening to the exterior on the ventral surface of the legs by a narrow passage.

(2) A coiled portion, which is again subdivided into several sections.

(3) A section with closely packed nuclei ending by a somewhat enlarged opening.

(4) The terminal portion, which consists of a thin-walled vesicle.

The last twelve pairs of these organs are all constructed in a very similar manner, while the two pairs situated in the fourth and fifth pairs of legs are considerably larger than those behind, and are in some respects very differently constituted.

It will be convenient to commence with one of the hinder nephridia. Such a nephridium from the ninth pair of legs is represented in Fig. 11. The external opening is placed at the outer end of a transverse groove at the base of one of the legs, while the main portion of the organ lies in the body cavity in the base of the leg, and extends into the trunk to about the level of the outer edge of the nerve-cord of its side. The external opening (o.s) leads into a narrow tube (s.d), which gradually dilates into a large sac (s). The narrow part is lined by small epithelial cells, which are directly continuous with and perfectly similar to those of the epidermis. The sac itself, which forms a kind of bladder or collecting vesicle for the organ, is provided with an extremely thin wall, lined with very large flattened cells. The second section of the nephridium is formed by the coiled tube, the epithelial lining of which varies slightly in the different parts. The third section (s.o.t), constitutes the most distinct portion of the whole organ. Its walls are formed of columnar cells almost filled by oval nuclei, which absorb colouring matters with very great avidity, and thus render this part extremely conspicuous. The nuclei are arranged in several rows. It ends by opening into a vesicle (Fig. 14, D), the wall of which is so delicate that it is destroyed when the nephridium is removed from the body, and consequently is not shown in Fig. 11.

Fig. 11.—Nephridium from the 9th pair of legs of P. capensis. o.s, External opening of segmental organ; p.f, internal opening of nephridium into the body cavity (lateral compartment); s, vesicle of segmental organ; s.c.1, s.c.2, s.c.3, s.c.4, successive regions of coiled portion of nephridium; s.o.t, third portion of nephridium broken off at p.f from the internal vesicle, which is not shown.

The fourth and fifth pairs are very considerably larger than those behind, and are in other respects peculiar. The great mass of each organ is placed behind the leg on which the external opening is placed, immediately outside one of the lateral nerve-cords. The external opening, instead of being placed near the base of the leg, is placed on the ventral side of the third ring (counting from the outer end) of the thicker portion of the leg. It leads into a portion which clearly corresponds with the collecting vesicle of the hinder nephridia. This part is not, however, dilated into a vesicle. The three pairs of nephridia in the three foremost pairs of legs are rudimentary, consisting solely of a vesicle and duct. The salivary glands are the modified nephridia of the segment of the oral papillae.

Generative Organs.

Male.—The male organs (Fig. 12) consist of a pair of testes (te), a pair of vesicles (v), vasa deferentia (v.d), and accessory glandular tubules (f). All the above parts lie in the central compartment of the body cavity. In P. capensis the accessory glandular bodies or crural glands of the last (17th) pair of legs are enlarged and prolonged into an elongated tube placed in the lateral compartment of the body cavity (a.g).

Fig. 12.—Male generative organs of Peripatus capensis, viewed from the dorsal surface. (After Balfour.) a.g, Enlarged crural glands of last pair of legs; F.16, 17, last pairs of legs; f, small accessory glandular tubes; p, common duct into which the vasa deferentia open; te, testis; v, seminal vesicle; v.c, nerve-cord; v.d, vas deferens.

The right vas deferens passes under both nerve-cords to join the left, and form the enlarged tube (p), which, passing beneath the nerve-cord of its side, runs to the external orifice. The enlarged terminal portion possesses thick muscular walls, and possibly constitutes a spermatophore maker, as has been shown to be the case in P. N. Zealandiae, by Moseley. In some specimens a different arrangement obtains, in that the left vas deferens passes under both nerve-cords to join the right.

Female.—The ovaries consist of a pair of tubes closely applied together, and continued posteriorly into the oviducts. The oviducts, after a short course, become dilated into the uteruses, which join behind and open to the exterior by a median opening. The ovaries always contain spermatozoa, some of which project through the ovarian wall into the body cavity. Spermatozoa are not found in the uterus and oviducts, and it appears probable that they reach the ovary directly by boring through the skin and traversing the body cavity.[^[6]] In the neotropical species there is a globular receptaculum seminis opening by two short ducts close together into the oviduct, and there is a small receptaculum ovorum with extremely thin walls opening into the oviduct by a short duct just in front of the receptaculum seminis. The epithelium of the latter structure is clothed with actively moving cilia. In the New Zealand species there is a receptaculum seminis with two ducts, but the receptacula ovorum has not been seen.

There appear to be present in most, if not all, the legs some accessory glandular structures opening just externally to the nephridia. They are called the crural glands.

DEVELOPMENT.

As stated at the outset, Peripatus is found in three of the great regions, viz. in Africa, in Australasia, and in South America and the West Indies. It is a curious and remarkable fact that although the species found in these various localities are really closely similar, the principal differences relating to the structure of the female generative organs and to the number of the legs, they do differ in the most striking manner in the structure of the ovum and in the early development. In all the Australasian species the egg is large and heavily charged with food-yolk, and is surrounded by a tough membrane. In the Cape species the eggs are smaller, though still of considerable size; the yolk is much less developed, and the egg membrane is thinner though dense. In the neotropical species the egg is minute and almost entirely devoid of yolk. The unsegmented uterine ovum of P. Novae-Zealandiae measures 1.5 mm. in length by .8 mm. in breadth; that of P. capensis is .56 mm. in length; and that of P. Trinidadensis .04 mm. in diameter. In correspondence with these differences in the ovum there are differences in the early development, though the later stages are closely similar.

Fig. 13.—A series of embryos of P. capensis. The hind end of embryos B, C, D is uppermost in the figures, the primitive streak is the white patch behind the blastopore. (After Sedgwick.) A, Gastrula stage, ventral view, showing blastopore. B, Older gastrula stage, ventral view, showing elongated blastopore and primitive streak. C, Ventral view of embryo with three pairs of mesoblastic somites, dumb-bell-shaped blastopore and primitive streak. D, Ventral view of embryo, in which the blastopore has completely closed in its middle portion, and given rise to two openings, the embryonic mouth and anus. The anterior pair of somites have moved to the front end of the body, and the primitive groove has appeared on the primitive streak. E, Side view of embryo, in which the hind end of the body has begun to elongate in a spiral manner, and in which the appendages have begun. At, antenna; d, dorsal projection; p.s, preoral somite. F, Ventral view of head of embryo intermediate between E and G. The cerebral grooves are wide and shallow. The lips have appeared, and have extended behind the openings of the salivary glands, but have not yet joined in the middle line. At, antennae; c.g, cerebral groove; j, jaws; j.s, swelling at base of jaws; L, lips; M, mouth; or.p, oral papillae; o.s, opening of salivary gland. G, Side view of older embryo with the full number of appendages, to show the position in which the embryos lie in the uterus.

But unfortunately the development has only been fully worked out in one species, and to that species—P. capensis—the following description refers. The ova are apparently fertilised in the ovary, and they pass into the oviducts in April and May. In May the brood of the preceding year are born, and the new ova, which have meanwhile undergone cleavage, pass into the uterus. There are ten to twenty ova in each uterus. The segmentation is peculiar, and leads to the formation of a solid gastrula, consisting of a cortex of ectoderm nuclei surrounding a central endodermal mass, which consists of a much-vacuolated tissue with some irregularly-shaped nuclei. The endoderm mass is exposed at one point—the blastopore (gastrula mouth). The central vacuoles of the endoderm now unite and form the enteron of the embryo, and at the same time the embryo elongates into a markedly oval form, and an opacity—the primitive streak—appears at the hind end of the blastopore (Fig. 13, B). This elongation of the embryo is accompanied by an elongation of the blastopore, which soon becomes dumb-bell shaped (Fig. 13, C). At the same time the mesoblastic somites (embryonic segments of mesoderm) have made their appearance in pairs at the hind end, and gradually travel forward on each side of the blastopore to the front end, where the somites of the anterior pair soon meet in front of the blastopore (Fig. 13, D). Meanwhile the narrow middle part of the blastopore has closed by a fusion of its lips, so that the blastopore is represented by two openings, the future mouth and anus. A primitive groove makes its appearance behind the blastopore (Fig. 13, D). At this stage the hind end of the body becomes curved ventrally into a spiral (Fig. 13, E), and at the same time the appendages appear as hollow processes of the body wall, a mesoblastic somite being prolonged into each of them. The first to appear are the antennae, into which the praeoral somites are prolonged. The remainder appear from before backwards in regular order, viz. jaw, oral papillae, legs 1-17. The full number of somites and their appendages is not, however, completed until a later stage. The nervous system is formed as an annular thickening of ectoderm passing in front of the mouth and behind the anus, and lying on each side of the blastopore along the lines of the somites. The praeoral part of this thickening, which gives rise to the cerebral ganglia, becomes pitted inwards on each side (Fig. 13, F, c.g). These pits are eventually closed, and form the hollow ventral appendages of the supra-pharyngeal ganglia of the adult (Fig. 9, d). The lips are formed as folds of the side wall of the body, extending from the praeoral lobes to just behind the jaw (Fig. 13, F, L). They enclose the jaws (j) mouth (M), and opening of the salivary glands (o.s), and so give rise to the buccal cavity. The embryo has now lost its spiral curvature, and becomes completely doubled upon itself, the hind end being in contact with the mouth (Fig. 13, G). It remains in this position until birth. The just-born young are from 10-15 mm. in length and have green antennae, but the rest of the body is either quite white or of a reddish colour. This red colour differs from the colour of the adult in being soluble in spirit.

The mesoblastic somites are paired sacs formed from the anterior lateral portions of the primitive streak (Fig. 13, C). As they are formed they become placed in pairs on each side of the blastopore. The somites of the first pair eventually obtain a position entirely in front of the blastopore (Fig. 13, D). They form the somites of the praeoral lobes. The full complement of somites is acquired at about the stage of Fig. 13, E.

Fig. 14.—A series of diagrams of transverse sections through Peripatus embryos to show the relations of the coelom at successive stages. (After Sedgwick.) A, Early stage: 1, gut; 2, mesoblastic somite; no trace of the vascular space; endoderm and ectoderm in contact. B, Endoderm has separated from the dorsal and ventral ectoderm. The somite is represented as having divided on the left side into a dorsal and ventral portion: 1, gut; 2, somite; 3, haemocoele. C, The haemocoele (3) has become divided up into a number of spaces, the arrangement of which is unimportant. The dorsal part of each somite has travelled dorsalwards, and now constitutes a small space (triangular in section) just dorsal to the gut. The ventral portion (2′) has assumed a tubular character, and has acquired an external opening. The internal vesicle is already indicated, and is shown in the diagram by the thinner black line: 1, gut; 2′, nephridial part of coelom; 3, haemocoele; 3′, part of haemocoele which will form the heart—the part of the haemocoele on each side of this will form the pericardium; 4, nerve-cord. D represents the conditions at the time of birth; numbers as in C, except 5, slime glands. The coelom is represented as surrounded by a thick black line, except in the part which forms the internal vesicle of the nephridium.

The relations of the somites is shown in Fig. 14, A, which represents a transverse section taken between the mouth and anus of an embryo of the stage of Fig. 13, D. The history of these somites is an exceedingly interesting one, and may be described shortly as follows:—They divide into two parts—a ventral part, which extends into the appendage, and a dorsal part (Fig. 14, B). The ventral part acquires an opening to the exterior just outside the nerve-cord, and becomes entirely transformed into a nephridium (Fig. 14, D, 2′). The dorsal part shifts dorsalwards and diminishes relatively in size (Fig. 14, C). Its fate differs in the different parts of the body. In the anterior somites it dwindles and disappears, but in the posterior part it unites with the dorsal divisions of contiguous somites of the same side, and forms a tube—the generative tube (Fig. 14, D, 2). The last section of this tube retains its connexion with the ventral portion of the somite, and so acquires an external opening, which is at first lateral, but soon shifts to the middle line, and fuses with its fellow, to form the single generative opening. The praeoral somite develops the rudiment of a nephridium, but eventually entirely disappears. The jaw somite also disappears; the oral papilla somite forms ventrally the salivary glands, which are thus serially homologous with nephridia. The perivisceral cavity of Peripatus is, as in all Arthropoda, a haemocoele. Its various divisions develop as a series of spaces between the ectoderm and endoderm, and later in the mesoderm. The mesoderm seems to be formed entirely from the proliferation of the cells of the mesoblastic somites. It thus appears that in Peripatus the coelom does not develop a perivisceral portion, but gives rise only to the renal and reproductive organs.

Synopsis of the Species of Peripatus.

Peripatus, Guilding.

Soft-bodied vermiform animals, with one pair of ringed antennae, one pair of jaws, one pair of oral papillae, and a varying number of claw-bearing ambulatory legs. Dorsal surface arched and more darkly pigmented than the flat ventral surface. Skin transversely ridged and beset by wart-like spiniferous papillae. Mouth anterior, ventral; anus posterior, terminal. Generative opening single, median, ventral, and posterior. One pair of simple eyes. Brain large, with two ventral hollow appendages; ventral cords widely divaricated, without distinct ganglia. Alimentary canal simple, uncoiled. Segmentally arranged, paired nephridia are present. Body cavity is continuous with the vascular system, and does not communicate with the paired nephridia. Heart tubular, with paired ostia. Respiration by means of tracheae. Dioecious; males smaller and generally less numerous than females. Generative glands tubular, continuous with the ducts. Viviparous. Young born fully developed. They shun the light, and live in damp places beneath stones, leaves, and bark of rotten stumps. They eject when irritated a viscid fluid through openings at the apex of the oral papillae.

Distribution: South Africa, New Zealand, and Australia, South America and the West Indies [and in Sumatra?].

South African Species.

With three spinous pads on the legs and two primary papillae on the anterior side of the foot, and one accessory tooth on the outer blade of the jaw; with a white papilla on the ventral surface of the last fully developed leg of the male. Genital opening subterminal, behind the last pair of fully-developed legs. The terminal unpaired portion of vas deferens short. Ova of considerable size, but with only a small quantity of food-yolk. (Colour highly variable, number of legs constant in same species (?).)

P. capensis (Grube).—South African Peripatus, with seventeen pairs of claw-bearing ambulatory legs. Locality, Table Mountain.

P. Balfouri (Sedgwick).—South African Peripatus, with eighteen pairs of claw-bearing ambulatory legs, of which the last pair is rudimentary. With white papillae on the dorsal surface. Locality, Table Mountain.

P. brevis (De Blainville).—South African Peripatus, with fourteen pairs of ambulatory legs. Locality, Table Mountain. (I have not seen this species. Presumably it has the South African characters.)

P. Moseleyi (Wood Mason).—South African Peripatus, with twenty-one and twenty-two pairs of claw-bearing ambulatory legs. Locality, near Williamstown, Cape Colony; and Natal.[^[7]]

Doubtful Species.

(1) South African Peripatus, with twenty pairs of claw-bearing ambulatory legs (Sedgwick). Locality, Table Mountain. (Also Peters, locality not stated.)

(2) South African Peripatus, with nineteen pairs of ambulatory legs (Trimen). Locality, Plettenberg Bay, Cape Colony. (Also Peters, locality not stated.)

Australasian Species.

With fifteen pairs of claw-bearing ambulatory legs, with three spinous pads on the legs, and a primary papilla projecting from the median dorsal portion of the feet. Genital opening between the legs of the last pair. Receptacula seminis present. Unpaired portion of vas deferens long and complicated. Ova large and heavily charged with yolk. (Colour variable, number of legs constant in same species (?).)

P. Novae Zealandiae (Hutton).—Australasian Peripatus, without an accessory tooth on the outer blade of the jaw, and without a white papilla on the base of the last leg of the male. New Zealand.

P. Leuckarti (Saenger).—Australasian Peripatus, with an accessory tooth on the outer blade of the jaw, and a white papilla on the base of the last leg of the male. Queensland.

Neotropical Species.

With four spinous pads on the legs, and the generative aperture between the legs of the penultimate pair. Dorsal white line absent. Primary papillae divided into two portions. Inner blade of jaw with gap between the first minor tooth and the rest. Oviducts provided with receptacula ovorum and seminis. Unpaired part of vas deferens very long and complicated. Ova minute, without food-yolk. (Colour fairly constant, number of legs variable in same species (?).)

P. Edwardsii.[^[8]]—Neotropical Peripatus from Caracas, with a variable number of ambulatory legs (twenty-nine to thirty-four). Males with twenty-nine or thirty legs, and tubercles on a varying number of the posterior legs. The basal part or the primary papilla is cylindrical.

P. Trinidadensis (n. sp.).—Neotropical Peripatus from Trinidad, with twenty-eight to thirty-one pairs of ambulatory legs, and a large number of teeth on the inner blade of the jaw. The basal portion of the primary papillae is conical.

P. torquatus (Kennel).— Neotropical Peripatus from Trinidad, with forty-one to forty-two pairs of ambulatory legs. With a transversely placed bright yellow band on the dorsal surface behind the head.

Doubtful Species.

The above are probably distinct species. Of the remainder we do not know enough to say whether they are distinct species or not. The following is a list of these doubtful species, with localities and principal characters:—

P. juliformis (Guilding).—Neotropical Peripatus from St. Vincent, with thirty-three pairs of ambulatory legs.

P. Chiliensis (Gay).—Neotropical Peripatus from Chili, with nineteen pairs of ambulatory legs.

P. demeraranus (Sclater).—Neotropical Peripatus from Maccasseema, Demerara, with twenty-seven to thirty-one pairs of ambulatory legs and conical primary papillae.

Peripatus from Cayenne (Audouin and Milne-Edwards).—With thirty pairs of legs. Named P. Edwardsii by Blanchard.

Peripatus from Valentia Lake, Columbia (Wiegmann).—With thirty pairs of legs.

Peripatus from St. Thomas (Moritz).—No description.

Peripatus from Colonia Towar, Venezuela (Grube).—With twenty-nine to thirty-one pairs of ambulatory legs. Named P. Edwardsii by Grube.

Peripatus from Santo Domingo, Nicaragua (Belt).—With thirty-one pairs of ambulatory legs.

Peripatus from Dominica (Angas).—Neotropical Peripatus, with twenty-six to thirty (Pollard) pairs of ambulatory legs.

Peripatus from Jamaica (Gosse).—With thirty-one and thirty-seven pairs of ambulatory legs.

Peripatus from Santaram.—Neotropical Peripatus, with thirty-one pairs of ambulatory legs.

Peripatus from Cuba.—No details.

Peripatus from Hoorubea Creek, Demerara (Quelch).—With thirty pairs of legs.

Peripatus from Marajo (Branner).—No details.

Peripatus from Utuado, Porto Rico (Peters).—With twenty-seven, thirty, thirty-one, and thirty-two pairs of legs.

Peripatus from Surinam (Peters).—No details.

Peripatus from Puerto Cabello, Venezuela (Peters).—With thirty and thirty-two pairs of legs.

Peripatus from Laguayra, Venezuela (Peters).—No details.

Peripatus Quitensis (Schmarda).—From Quito, with thirty-six pairs of legs.

Peripatus from Sumatra (?).

P. Sumatranus (Horst).—Peripatus from Sumatra, with twenty-four pairs of ambulatory legs, and four spinous pads on the legs. The primary papillae of the neotropical character with conical bases. Generative opening between the legs of the penultimate pair. Feet with only two papillae.[^[9]]

Summary of Distribution

Distribution of the South African Species—

Slopes of Table Mountain, neighbourhood of Williamstown, Plettenberg Bay—Cape Colony—Natal.

Distribution of the Australasian Species—

Queensland—Australia.

North and South Islands—New Zealand.

Oriental Region (?)—

Sumatra.

Distribution of the Neotropical Species—

Nicaragua.

Valencia Lake, Caracas, Puerto Cabello, Laguayra, Colonia Towar—Venezuela.

Quito—Ecuador.

Maccasseema, Hoorubea Creek—Demerara.

Surinam (Peters).

Cayenne.

Santarem, Marajo, at the mouth of the Amazon—Brazil.

Chili.

And in the following West Indian Islands—Cuba, Dominica, Porto Rico (Peters), Jamaica, St. Thomas, St. Vincent, Trinidad.

MYRIAPODA

BY

F. G. SINCLAIR, M.A.
(FORMERLY F. G. HEATHCOTE)

Trinity College, Cambridge.

CHAPTER II

MYRIAPODA

INTRODUCTION–HABITS–CLASSIFICATION–STRUCTURE–CHILOGNATHA–CHILOPODA–SCHIZOTARSIA–SYMPHYLA–PAUROPODA–EMBRYOLOGY–PALAEONTOLOGY.

Tracheata with separated head and numerous, fairly similar segments. They have one pair of antennae, two or three pairs of mouth appendages, and numerous pairs of legs.

The Myriapoda are a class of animals which are widely distributed, and are represented in almost every part of the globe. Heat and cold alike seem to offer favourable conditions for their existence, and they flourish both in the most fertile and the most barren countries.

They have not attracted much notice until comparatively recent times. Compared with Insects they have been but little known. The reason of this is not hard to find. The Myriapods do not exercise so much direct influence on human affairs as do some other classes of animals; for instance, Insects. They include no species which is of direct use to man, like the silkworm or the cochineal insect, and they are of no use to him as food. It is true that they are injurious to his crops. For instance, the species of Millepede known as the "wire worm"[^[10]] is extremely harmful; but this has only attracted much notice in modern times, when land is of more value than formerly, and agriculture is pursued in a more scientific manner, and the constant endeavour to get the utmost amount of crop from the soil has caused a minute investigation into the various species of animals which are noxious to the growing crop. The species of Myriapoda best known to the ancients were those which were harmful to man on account of their poisonous bite.

Some writers have supposed that the word which is translated "mole" in the Bible (Lev. xi. 30) is really Scolopendra (a genus of Centipede), and, if this is so, it is the earliest mention of the Myriapods. They were rarely noticed in the classical times; almost the only mention of them is by Ælian, who says that the whole population of a town called Rhetium were driven out by a swarm of Scolopendras. Pliny tells us of a marine Scolopendra, but this was most probably a species of marine worm.

Linnaeus included Myriapods among the Insects; and the writers after him till the beginning of this century classed them with all sorts of Insects, with Spiders, Scorpions, and even among Serpents. It was Leach who first raised them to the importance of a separate class, and Latreille first gave them the name of Myriapoda, which they have retained ever since.

Myriapods are terrestrial animals, crawling or creeping on the ground or on logs of wood, or even under the bark of trees. There is, however, a partial exception to this; various naturalists have from time to time given descriptions of marine Centipedes. These are not found in the sea, but crawl about on the shore, where they are submerged by each tide. Professor F. Plateau has given an account of the two species of Myriapods that are found thus living a semi-aquatic life. They are named Geophilus maritimus and Geophilus submarinus, and Plateau found that they could exist in sea water from twelve to seventy hours, and in fresh water from six to ten days. They thus offer a striking example of the power that their class possess of existing under unfavourable circumstances.

With regard to their habits the different species differ very considerably. On the one hand we have the Chilopoda, or Centipedes, as they are called in this country, active, swift, and ferocious; living for the most part in dark and obscure places, beneath stones, logs of wood, and dried leaves, etc., and feeding on living animals. On the other hand, we have the Chilognatha, or Millepedes, distinguished by their slow movements and vegetable diet; inoffensive to man, except by the destruction they occasion to his crops, and having as a means of defence no formidable weapon like the large poison claws of the Centipedes, but only a peculiarly offensive liquid secreted by special glands known by the unpleasant though expressive name of "stink glands," or by the more euphonious Latin name of glandulae odoriferae.

As a general rule the larger species of Myriapods are found in the hotter climates, some of the tropical species being very large, and some, among the family of the Scolopendridae, extremely poisonous; and it is even said that their bite is fatal to man.

Fig. 15.—Scolopendra obscura. (From C. L. Koch, Die Myriapoden.)

If, however, the Centipede is sometimes fatal to man, it does not always have it its own way, for we read of man making food of Centipedes. It is hard to believe that any human being could under any circumstances eat Centipedes, which have been described by one naturalist as "a disgusting tribe loving the darkness." Nevertheless, Humboldt informs us that he has seen the Indian children drag out of the earth Centipedes eighteen inches long and more than half an inch wide and devour them.

Fig. 16.—Chordeuma sylvestre. (From C. L. Koch, Die Myriapoden.)

This, I believe, is the only account of human beings using the Myriapoda as food, if we except the accounts of the religious fanatics among the African Arabs, who are said to devour Centipedes alive; though this is not a case of eating for pleasure, for the Scolopendras are devoured in company with leaves of the prickly pear, broken glass, etc., as a test of the unpleasant things which may be eaten under the influence of religious excitement.

A cold climate, however, is not fatal to some fairly large species of Centipedes. A striking instance of this came under my own observation some years ago. In 1886 I was travelling in the island of Cyprus—the "Enchanted Island," as Mr. Mallock calls it in his book written about the same time—with the intention of observing its natural history. This island consists of a broad flat country crossed by two mountain ranges of considerable height, thus offering the contrast of a hot climate in the plains and a cold climate in the mountains. On the plain country I found among the Myriapoda that the most common species were a large Scolopendra and a large Lithobius. The Scolopendra was fairly common, living for the most part under large stones, and it was a pleasant task to search for them in a ruined garden near Larnaca.

This garden was made for the public, and is situated about a quarter of a mile from the old town of Larnaca. It has been suffered to fall into decay, and is now quite neglected. Mr. Mallock has described many beautiful scenes in his book, but I think he could have found few more beautiful than this old garden with its deserted gardener's house, now a heap of ruins, but overgrown with masses of luxuriant vegetation, with beautiful flowers peeping out here and there as if charitably endeavouring to hide the negligence of man, and to turn the desolation into a scene of beauty. I got several prizes in this garden, but found the Myriapods were principally represented by the species I have mentioned.

After leaving Larnaca I rode across the plain country through blazing heat, which was rapidly parching up the ground to a uniform brown colour. At every stopping-place I found the same species of Scolopendra and of Lithobius. After a few days I began to get up among the mountains of the northern range, and the burning heat of the treeless plain was gradually exchanged for the cool shade of the pine-trees and the fresh air of the mountains. As I ascended higher and higher the temperature grew cooler till I reached the top of Mount Troodos, the ancient Olympus. Here in the month of May the snow still lingered in white patches, and the air was clear and cold. I remained on the top of Troodos for a week, while I made a close examination of the fauna to be found there. I was much surprised to find the identical species of Scolopendra and Lithobius with which I had become acquainted in the heat of the low country, quite at home among the snow, and as common as in, what I should have imagined to be, the more congenial climate. Nor were they any the less lively. Far from exhibiting any sort of torpor from the cold, the first one which I triumphantly seized in my forceps wriggled himself loose and fastened on my finger with a vigour which made me as anxious to get rid of him as I had formerly been to secure him. However, he eventually went into my collecting box.

On the whole, we may say that the Chilopoda are most largely represented in the hotter climates, where they find a more abundant diet in the rich insect life of the tropical and semi-tropical countries. The more brightly-coloured Myriapods, too, are for the most part inhabitants of the warmer countries. The ease with which they are introduced into a country in the earth round plants, and in boxes of fruit, may account to a great extent for the wide distribution of the various species in different countries. Mr. Pocock, who examined the Myriapods brought back from the "Challenger" Expedition, informs us that of ten species brought from Bermuda, four had been introduced from the West Indies. There is no doubt that animals which can bear changes of temperature and deprivation of food, and even a short immersion in the water, are well calculated to be introduced into strange countries in many unexpected ways.

As might be expected from a class of animals so widely distributed, Myriapods show an almost infinite variety of size and colour. We find them so small that we can hardly see them with the naked eye, as in the case of the tiny Polyxenus, the Pauropidae, and the Scolopendrellidae. We also find them more than six inches in length, as the larger species of Scolopendridae. I am afraid we must dismiss as an exaggeration an account of Centipedes in Carthagena a yard in length, and more than six inches in breadth. The giver of this account—Ulloa—informs us that the bite of this gigantic serpent-like creature is mortal if a timely remedy be not applied. It is certainly extremely probable that the bite of a Centipede of this size would be fatal to any one. Some Centipedes are short and broad, and composed of few segments, as Glomeris; some are long and thin, with more than a hundred segments, as Geophilus. They may be beautifully coloured with brilliant streaks of colour, as in some of the Julidae or Polydesmidae, or may be of a dull and rusty iron colour, or quite black.

One of the strangest peculiarities found among Myriapods is that some of them (e.g. Geophilus electricus) are phosphorescent. As I was walking one summer evening near my home in Cambridgeshire I saw what I thought was a match burning. Looking more closely, I saw it move, and thinking it was a glow-worm I picked it up, and was surprised to find that it was a Geophilus shining with a brilliant phosphorescent light. I let it crawl over my hand, and it left a bright trail of light behind it, which lasted some time. I have been told that this species is common in Epping Forest; also in Cambridgeshire.[^[11]]

Besides G. electricus, G. phosphoreus has been described as a luminous species by Linnaeus, on the authority of a Swedish sea captain, who asserted that it dropped from the air, shining like a glow-worm, upon his ship when he was sailing in the Indian Ocean a hundred miles from land.

What the use of this phosphorescence may be is not known with any degree of certainty. It may be either a defence against enemies, or else a means of attracting the two sexes to one another.

The places which the Myriapods select for their habitation vary as much as their colour and size, though, with a few exceptions, they chose dark and obscure places. A curious species of Myriapod is Pseudotremia cavernarum (Cope), which is found in certain caves in America. The peculiar life it leads in these caves seems to have a great influence on its colour, and also affects the development of its eyes. Mr. Packard's account of them is worth quoting: "Four specimens which I collected in Little Wyandotte cave were exactly the same size as those from Great Wyandotte cave. They were white tinged, dusky on the head and fore part of the body. The eyes are black and the eye-patch of the same size and shape, while the antennae are the same.

"Six specimens from Bradford cave, Ind. (which is a small grotto formed by a vertical fissure in the rock, and only 300 to 400 yards deep), showed more variation than those from the two Wyandotte caves. They are of the same size and form, but slightly longer and a little slenderer.... The antennae are much whiter than in those from the Wyandotte caves, and the head and body are paler, more bleached out than most of the Wyandotte specimens.... It thus appears that the body is most bleached and the eyes the most rudimentary in the Bradford cave, the smallest and most accessible, and in which consequently there is the most variation in surroundings, temperature, access of light and changed condition of air. Under such circumstances as these we should naturally expect the most variation."[^[12]]

A strong contrast to these animals is afforded us by the Scutigeridae (Schizotarsia). They are unknown in this country, but abound in some of the Mediterranean countries and in parts of Africa. They remind one strongly of spiders, with their long legs and their peculiar way of running on stones and about the walls of houses.

Fig. 17.—Cermatia (Scutigera) variegata. (From C. L. Koch, Die Myriapoden.)

Some years ago I was in Malta, and I used to go and watch them on the slopes outside Valetta, where they were to be found in great numbers. They used to come out from beneath great stones and run about rapidly on the ground or on the stones and rubbish with which the ground was covered, now and again making a dart at some small insect which tempted them, and seemingly not minding the blazing sun at all. As might be expected from their habits, their eyes, far from being rudimentary, like those of the cave-living Pseudotremia, or absent like those of the Polydesmidae, or of our own Cryptops, are highly developed, and form the only example among the Myriapods of what are known as facetted eyes. The Scutigeridae are also remarkable among Myriapods for the possession of a peculiar sense-organ which is found in no other Myriapod.

The Myriapods most numerous in our own country are Lithobius and Julus. Lithobius, which will be described later on, may be found in almost any garden under dried leaves, stones, etc. Julus, the common wire-worm, is found crawling on plants and leaves and under the bark of trees, and does a good deal of damage in a garden. Polydesmus is also frequently found in great numbers, and usually a great many of them together. Glomeris is also found, though it is not so common as the first two mentioned animals. Geophilus is also common, and especially in the south of England. Scolopendridae are only represented by a single genus, Cryptops, which is not very common, though by no means rare. The best place to find them is in manure heaps. The animals of this species are small compared to most Scolopendras, and have the peculiarity of being without any eyes.

Scutigera is unrepresented in this country. One was found in Scotland some years ago by Mr. Gibson Carmichael, but was shown to have been imported, and not bred in the place.

The means of defence possessed by these animals also differ very much in the different species of Myriapods. In the Centipedes the animals are provided with a powerful weapon in the great poison claws which lie just beneath the mouth, and which are provided with large poison glands, which supply a fluid which runs through a canal in the hard substance of the claw and passes into the wound made by the latter. The effect of this fluid is instantaneous on the small animals which form the food of the Centipedes. I have myself watched Lithobius in this country creep up to a blue-bottle fly and seize it between the poison claws. One powerful nip and the blue-bottle was dead, as if struck by lightning. I have also seen them kill worms and also other Lithobius in the same way. When another Lithobius is wounded by the poison claws it seems to be paralysed behind the wound. The Millepedes, on the other hand, have no such offensive and defensive weapon. They rely for protection on the fluid secreted by the stigmata repugnatoria (or glandulae odoriferae) mentioned before. This fluid has been shown to contain prussic acid, and has a very unpleasant odour.

Fig. 18.—Polyxenus lagurus (From C. L. Koch, Die Myriapoden).

Most of the Millepedes are provided with these glands; but in the cave Myriapods mentioned before, the animals have not to contend against so many adversaries, and these glands almost disappear. Other Myriapods defend themselves by means of the long and stiff bristles with which they are provided, e.g. the little Polyxenus. This means of defence seems to have been more common among the fossil Myriapods than among those still living. Variations in the shape and size of the limbs are numerous, as might be expected in so large a class of animals. One of the most curious of such variations is found in a Centipede of the Scolopendra tribe, called Eucorybas, in which the last limbs are flattened out and provided with paddle-shaped lobes. The use of these is unknown, but it is probable that they are concerned in some way with the breeding habits of the animal. The habits of the Myriapods connected with their breeding are most interesting, but have been very insufficiently investigated. There is no doubt that a full inquiry into all such habits would be of great interest, and would help to answer some of the problems which are still unsolved in these forms. My own observations refer to two forms—Julus terrestris among the Millepedes, and Lithobius forficatus among the Centipedes. Julus terrestris is one of the most common of the English Millepedes, and can be easily obtained. I kept them in large shallow glass vessels with a layer of earth at the bottom, and thus was able easily to watch the whole process. They breed in the months of May, June, and July. The female Julus when about to lay her eggs sets to work to form a kind of nest or receptacle for her eggs. She burrows down into the earth, and at some distance below the surface begins the work. She moistens small bits of earth with the sticky fluid secreted by her salivary glands, which become extraordinarily active in the spring. She works up these bits of earth with her jaws and front legs till they are of a convenient size and shape, and places them together. When complete, the nest is shaped like a hollow sphere, the inside being smooth and even, while the outside is rough and shows the shape of the small knobs of earth of which it is composed. She leaves a small opening in the top. The size of the whole nest is about that of a small nut. When she is ready to lay her eggs she passes them through the hole in the top, and usually lays about 60 to 100 eggs at a time. The eggs, which are very small, are coated with a glutinous fluid which causes them to adhere together. When they are all laid she closes up the aperture with a piece of earth moistened with her saliva; and having thus hermetically sealed the nest, she leaves the whole to its fate. The eggs hatch in about twelve days.

A naturalist named Verloef has lately found that the males of some Julidae undergo certain changes in the form of the legs and other organs in autumn and spring. These changes are probably connected with the breeding of the animal, and remind us of the changes undergone during the breeding season by salmon among the fishes.

Julus breed very readily if carefully attended to and well supplied with food. If they cannot obtain the food they like they will not breed so well. I found that sliced apples with leaves and grass formed the best food for them.

The process in the case of Lithobius is much harder to watch. Lithobius is not so plentiful as Julus terrestris, and the animals are more impatient of captivity, more shy in their habits, and do not breed so readily.

In January 1889 I was given the use of a room in the New Museums at Cambridge, and was allowed to fit it up as I liked, so that I was able to try the effect of different degrees of light and darkness, and of different degrees of warmth. I succeeded in observing the whole process. The female Lithobius is furnished with two small movable hooks at the end of the under surface of the body close to the opening of the oviduct. These small hooks have been observed by many naturalists, but their use has, so far as I know, never been described before. They play an important part in the proceedings following the laying of the egg. The time of breeding in Lithobius is rather later than in Julus, and begins about June and continues till August. There are first of all some convulsive movements of the last segments of the body, and then in about ten minutes the egg appears at the entrance of the oviduct. The egg is a small sphere (about the size of a number five shot), rather larger than that of Julus, and is covered with a sticky slime secreted by the large glands inside the body, usually called the accessory glands. When the egg falls out it is received by the little hooks, and is firmly clasped by them. This is the critical moment in the existence of the Lithobius into which the egg is destined to develop. If a male Lithobius sees the egg he makes a rush at the female, seizes the egg, and at once devours it. All the subsequent proceedings of the female seem to be directed to the frustration of this act of cannibalism. As soon as the egg is firmly clasped in the little hooks she rushes off to a convenient place away from the male, and uses her hooks to roll the egg round and round until it is completely covered by earth, which sticks to it owing to the viscous material with which it is coated; she also employs her hind legs, which have glands on the thighs, to effect her purpose. When the operation is complete the egg resembles a small round ball of mud, and is indistinguishable from the surrounding soil. It is thus safe from the voracious appetite of the male, and she leaves it to its fate. The number of eggs laid is small when compared with the number laid by Julus.

The food in the case of Lithobius consisted of worms and blue-bottles, which were put alive into the glass vessel containing the Lithobius. I tried raw meat chopped up, but they did not thrive on it in the same way that they did on the living animals. I also put into their vessel bits of rotten wood containing larvae of insects, etc.

I have succeeded in bringing back some specimens of Polydesmus alive from Madeira, and in getting them to breed in this country—of course in artificial warmth—and their way of laying eggs and making a nest resembles that of Julus. Geophilus has one curious habit in connexion with the fertilisation of the female. The male spins a web and deposits in the middle of it a single spermatophore, and the female comes to the web to be fertilised. The Scolopendridae are said to bring forth their young alive, but I think the evidence for this is unsatisfactory. What have been taken for the young Scolopendrae are perhaps the large spermatophores of the male, which are not unlike a larval Myriapod in size and shape. I have never been able to observe the process of breeding in this family. I have had the spermatophores sent me from Gibraltar as "eggs," but a little examination soon showed me their real character.

The mode of progression in the Myriapods differs considerably, as might be expected in a class in which the number of legs varies to such an extent. The swiftest among them are the Scutigeridae with their long spider-like legs. The Scolopendridae are also able to move with considerable rapidity, and are also able to move tail forward almost as well as in the ordinary manner. Where there are such a number of legs it becomes a curious question as to the order in which the animal moves them; and though several people have endeavoured to find this out, the number of legs to be moved and the rapid movements have rendered accurate observation impossible.

Some years ago Professor E. Ray Lankester tried to study the order in which the legs of Centipedes moved, and came to the conclusion (recorded in an amusing letter in Nature, 23rd May 1889) that if the animal had to study the question itself, it would not get on at all. He finishes his letter with the following verses:—

A Centipede was happy quite

Until a toad in fun

Said, "Pray which leg moves after which?"

This raised her doubts to such a pitch,

She fell exhausted in the ditch,

Not knowing how to run.

The progression of Millepedes is much slower than that of the Centipedes, and it is remarkable that when the animal is in motion a sort of wave runs down the long fringe-like row of feet. I have endeavoured to make out this motion, but have never been able to understand it satisfactorily. My belief was that the feet were moved in sets of five.

This wave-like peculiarity of motion is described in a curious old book, An Essay towards a Natural History of Serpents. Charles Owen, D.D. London, 1742: "The Ambua, so the natives of Brazil call the Millepedes and the Centipedes, are serpents. Those reptiles of thousand legs bend as they crawl along, and are reckoned very poisonous. In these Multipedes the mechanism of the body is very curious; in their going it is observable that on each side of their bodies every leg has its motion, one regularly after another, so that their legs, being numerous, form a kind of undulation, and thereby communicate to the body a swifter progression than one could imagine where so many short feet are to take so many short steps, that follow one another rolling on like the waves of the sea."

Before proceeding to the classification of Myriapods, which will form the next part of this account, a few words on the common names for them may not be without interest.

In English we have the names Centipede and Millepede, and the Continental nations have similar names implying the possession of a hundred or a thousand legs, as the German "Tausendfüsse" and the French "Millepieds." Of course these are general words, simply implying the possession of a great number of legs. But we have also among the peasantry a name for Centipedes which conveys a much more accurate idea of the number. The people of the eastern counties (I daresay the term is more widely spread) call them "forty legs." This is not quite accurate, but as Lithobius has 17 legs on each side, and Scolopendra (Cryptops is the English species) has 21 on each side, it is a better approximation than Centipede. But another country has a still more accurate term. I found some Scolopendra in Beyrout, and asked my native servant what he called them. He gave them what I afterwards found was the common Arab name for them, "‘arba wál ‘arbarin," forty-four legs. Now the Scolopendras, which in hotter climates are the chief representatives of the Centipedes, have actually forty-two legs, or, if the poison claws are counted, forty-four. In looking up the Arab term for Centipede I came across a curious description given of them by Avicenna, the great Arabian physician: "This is an animal known for its habit of going into ears. For the most part it is a palm's length" [about four inches, which is the average length of many species]. "On each side of the body it has twenty-two feet, and moves equally well either backwards or forwards."

With regard to its alleged habit of going into ears, the learned Arabian has evidently made a false imputation on the character of our animal, and has probably relied too much on the stories told him. He has also exaggerated in stating that it goes equally well either backwards or forwards. Some Centipedes can go backwards very easily and well, though not so well as forwards. Perhaps he preferred examining dead specimens, which afford an easy opportunity of counting their legs, to experimenting with living animals, which might have resented liberties taken with them.

The Persians have several words for them, less accurate than the Arabs and more like our own terms. For instance, they call them "Hazarpa," or thousand feet, like our Millepedes; also "Sadpa," or hundred feet, equivalent to our Centipedes. Another term resembles our common term before mentioned, "Chehlpa," forty feet. A more figurative term is "tasbih dud," a worm resembling a rosary with a hundred beads; this word is translated in Richardson's Persian Dictionary as "a venomous insect having eight feet and a piked tail."

Classification of the Myriapoda.

Two of the principal writers on the classification of the Myriapods are Koch and Latzel, both of whom have classified the whole group. I do not wish for a moment to undervalue the many authors who have done excellent work on the classification of different groups and families, but I wish here to give an outline of a classification of the whole class, and I naturally have recourse to the authors who have treated the subject as a whole.

Koch's two works, the System der Myriapoden[^[13]] and Die Myriapoden,[^[14]] cover the whole range of the class, and his divisions are clearly marked out and are easily understood, but both works are comparatively old. He does not include the Scolopendrellidae or the Pauropidae, which are now included by all naturalists in the Myriapoda. Latzel is a more recent writer, and though his work is entitled The Myriapods of the Austro-Hungarian Empire,[^[15]] he gives much information about Myriapods not found in Europe, and his work is fairly entitled to be considered as embracing the whole class. He divides the Myriapods into four Orders, including the Scolopendrellidae and Pauropidae. On the whole, I think it will be better here to take the classification of Koch, and to add to it the two Orders before mentioned, viz. Symphyla containing one family the Scolopendrellidae, and Pauropoda with one family the Pauropidae.

The Orders are as follows:—

Order I. Chilognatha (= Diplopoda)

Antennae 7 joints, three anterior body rings with one pair of legs to each ring. Posterior rings with two pairs of legs to each. Genital organs opening ventrally on the anterior rings of the posterior part of the body, i.e. on one of the anterior of the segments bearing two pairs of legs; usually the 7th.

This Order is divided into eight families:—

Family 1. Polyxenidae.

Ten body rings, not counting the neck-plate. Thirteen pairs of limbs. Eyes hard to find, on the lateral corner of the head (Fig. 18, p. [37]).

Family 2. Glomeridae.

11 body rings. 17 pairs of legs. Eyes arranged in a row curved outwards.

Fig. 19.—Glomeris marginata. (From C. L. Koch, Die Myriapoden.)

Family 3. Sphaerotheriidae.

12 body rings. 19 pairs of legs. Eyes crowded together in a cluster.

Fig. 20.—Sphaerotherium grossum. (From C. L. Koch, Die Myriapoden.)

Family 4. Julidae.

Body cylindrical. More than 30 body rings. Many eyes crowded together in a cluster.

Fig. 21.—Julus nemorensis. (From C. L. Koch, Die Myriapoden.)

Family 5. Blanjulidae.

Thin cylindrical body with more than 30 body rings. Eyes either absent or in a simple row beneath the edge of the forehead.

Fig. 22.—Blanjulus guttulatus. (From C. L. Koch, Die Myriapoden.)

Family 6. Chordeumidae.

Resemble the Polydesmidae (Fam. 7), but the head is longer and less rounded in the forehead. The antennae are placed more at the side of the head. Eyes small and numerous, in a cluster. Body rings always 30 (Fig. 16).

Family 7. Polydesmidae.

Body cylindrical, with a lobe or keel on the posterior part of the upper surface of the body ring. Always 19 body rings. No eyes.

Fig. 23.—Polydesmus collaris. (From C. L. Koch, Die Myriapoden.)

Family 8. Polyzoniidae.

Body with varying number of rings arched transversely downwards and sharp at the sides. The anterior part of the ring somewhat hidden. The eyes in a simple row. The stigmata very small and placed near the lateral corner of the body ring. Head small in proportion to the body.

Fig. 24.—Polyzonium germanicum. (From C. L. Koch, Die Myriapoden.)

Order II. Chilopoda (or Syngnatha).

Antennae with many joints, at least 14. Only one pair of legs to each body ring. The genital opening on the last ring of the body. Bases of the legs widely separate.

There are four families in this Order:—

Family 1. Lithobiidae.

Body with 9 principal and 6 subsidiary rings. On both principal and subsidiary rings one pair of legs, except on the last ring of the body. Many eyes; the posterior ones large and kidney-shaped. The antennae with many rings.