HYMENOPTERA PETIOLATA—PARASITIC HYMENOPTERA—CYNIPIDAE OR GALL-FLIES
—PROCTOTRYPIDAE—CHALCIDIDAE—ICHNEUMONIDAE—BRACONIDAE—STEPHANIDAE
—MEGALYRIDAE—EVANIIDAE—PELECINIDAE—TRIGONALIDAE 519
INDEX 567
SCHEME OF THE CLASSIFICATION (RECENT FORMS) ADOPTED IN THIS BOOK
PROTOTRACHEATA
PERIPATUS (p. 1)
MYRIAPODA
Order. Family.
CHILOGNATHA POLYXENIDAE (p. 43).
(= DIPLOPODA) 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, Family.
or Sub-Order.
APTERA THYSANURA CAMPODEIDAE (p. 183).
(p. 180) (p. 182) JAPYGIDAE (p. 184).
MACHILIDAE (p. 184).
LEPISMIDAE (p. 185).
COLLEMBOLA LIPURIDAE (p. 190).
(p. 189) PODURIDAE (p. 190).
SMYNTHURIDAE (p. 191).
Order. Division, Series, Family. Tribe or
or Sub-Order. Sub-Family.
ORTHOPTERA ORTHOPTERA FORFICULIDAE (p. 202).
(p. 198) CURSORIA
HEMIMERIDAE (p. 217).
BLATTIDAE Ectobiides.
(p. 220) Phyllodromiides.
Nyctiborides.
Epilamprides.
Periplanetides.
Panchlorides.
Blaberides.
Corydiides.
Oxyhaloides.
Perisphaeriides.
Panesthiides.
? Geoscapheusides.
MANTIDAE Amorphoscelides.
(p. 242) Orthoderides.
Mantides.
Harpagides.
Vatides.
Empusides.
PHASMIDAE Lonchodides.
(p. 260) Bacunculides.
Bacteriides.
Necroscides.
Clitumnides.
Acrophyllides.
Cladomorphides.
Anisomorphides.
Phasmides.
Aschipasmides.
Bacillides.
Phylliides.
ORTHOPTERA ACRIDIIDAE Tettigides.
SALTATORIA (p. 279) Pneumorides.
Mastacides.
Proscopiides.
Tryxalides.
Oedipodides.
Pyrgomorphides.
Pamphagides.
Acridiides.
LOCUSTIDAE Phaneropterides.
(p. 311) Meconemides.
Mecopodides.
Prochilides.
Pseudophyllides.
Conocephalides.
Tympanophorides.
Sagides.
Locustides.
Decticides.
Callimenides.
Ephippigerides.
Hetrodides.
Gryllacrides.
Stenopelmatides.
GRYLLIDAE Tridactylides.
(p. 330) Gryllotalpides.
Myrmecophilides.
Gryllides.
Oecanthides.
Trigonidiides.
Eneopterides.
Order. Division, Series, Family. Tribe or Group.
or Sub-Order. Sub-Family.
NEUROPTERA MALLOPHAGA Leiotheides.
(p. 345) Philopterides.
PSEUDO- EMBIIDAE (p. 351).
NEUROPTERA TERMITIDAE (p. 356).
PSOCIDAE (p. 390).
NEUROPTERA PERLIDAE (p. 398).
AMPHIBIO-
TICA ODONATA Anisopterides Gomphinae.
(p. 409) Cordulegasterinae.
Aeschninae.
Corduliinae.
Libellulinae.
Zygopterides Calepteryginae.
Agrioninae.
EPHEMERIDAE (p. 429).
NEUROPTERA SIALIDAE Sialides
PLANIPENNIA (p. 444) Raphidiides.
PANORPIDAE (p. 449).
HEMEROBIIDAE Myrmeleonides (p. 454).
(p. 453) Ascalaphides Holophthalmi.
(p. 459) Schizophthalmi.
Nemopterides (p. 462).
Mantispides (p. 463).
Hemerobiides Dilarina.
(p. 465) Nymphidina.
Osmylina.
Hemerobiina.
Chrysopides (p. 469).
Coniopterygides (p. 471).
TRICHOPTERA PHRYGANEIDAE Phryganeides (p. 480).
(p. 473) Limnophilides (p. 481).
Sericostomatides (p. 482).
Leptocerides (p. 482).
Hydropsychides (p. 482).
Rhyacophilides (p. 483).
Hydroptilides (p. 484).
HYMENOPTERA HYMENOPTERA CEPHIDAE (p. 504).
(p. 487) SESSILI- ORYSSIDAE (p. 506).
VENTRES SIRICIDAE (p. 507).
TENTHREDINIDAE (p. 510).
HYMENOPTERA CYNIPIDAE (p. 523).
PETIOLATA PROCTOTRYPIDAE (p. 533).
(part) 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.
{3}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.
{4}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
{5}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).
{6}[Illustration: FIG. 1.—_Peripatus capensis_, drawn from life. Life size.
(After Sedgwick.)]
[Illustration: 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 {7}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.
[Illustration: 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 {8}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.
[Illustration: 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.]
[Illustration: 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 {9}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 {10}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 {11}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).
[Illustration: 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
{12}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_).
[Illustration: 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 {13}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, {14}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 {15}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.
[Illustration: 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.
{16}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 {17}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.
[Illustration: 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.
{18}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_).
[Illustration: 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 {19}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.
{20}[Illustration: 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 {21}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.
{22}[Illustration: 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 {23}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?].
{24}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
{25}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.
{26}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.
{29}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 {30}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 {31}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.
[Illustration: 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.
[Illustration: 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.
{32}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 {33}_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 {34}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
{35}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.
[Illustration: 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 {36}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.
{37}[Illustration: 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. {38}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 {39}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.
{40}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 {41}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.
{42}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:—
{43}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.
[Illustration: 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.
[Illustration: 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.
[Illustration: FIG. 21.—_Julus nemorensis._ (From C. L. Koch, _Die
Myriapoden_.)]
{44}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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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:—
{45}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.
[Illustration: FIG. 25.—_Lithobius erythrocephalus._ (From C. L. Koch,
_Die Myriapoden_.)]
Family 2. _Scolopendridae._
Body with 21 or 23 rings, no intermediate rings. Every ring with one pair
of legs. The last pair very long. Last pair at the point of the last
ring. Four or no eyes. Antennae with 17 or 20 joints. (Fig. 15, p. 31).
Family 3. _Notophilidae._
[Illustration: FIG. 26.—_Notophilus taeniatus._ (From C. L. Koch, _Die
Myriapoden_.)]
Body very long, 200 to 350 rings; alternate principal and subsidiary
rings. A pair of legs to each principal ring. No eyes. Maxillary palps
{46}very thick. Compact or very short limbs. The terminal point of the
last limb without claws.
Family 4. _Geophilidae._
Body long, 80 to 180 rings, principal and subsidiary. No eyes. The
maxillary palps not compact, and with first joint large. Last joint of
the last pair of legs with a sharp claw.
[Illustration: FIG. 27.—_Geophilus longicornis._ (From C. L. Koch, _Die
Myriapoden_.)]
Order III. SCHIZOTARSIA.
The tarsi of all the legs multiarticulate. The eyes facetted. Peculiar
sense organ beneath the head.
Family 1. _Cermatiidae_ (_Scutigeridae_)
Antennae with unequal number of joints. Body rings, each with one pair of
legs. Dorsal scutes not so large as ventral. Limbs long and
multiarticulate. (Fig. 17, p. 35).
Order IV. SYMPHYLA.
Myriapods resembling Thysanura. A pair of limbs to each segment. The
antennae are simple and multiarticulate with unequal joints. Eyes few.
Mandibles short. One pair of maxillae. No maxillipedes. Genital orifice in
the last segment of the body. A single pair of tracheae. Two abdominal
glands on the posterior part of the body. Two caudal appendages. Free
dorsal scutes. Ventral scutes often with parapodia.
Family 1. _Scolopendrellidae._
With the characters of the Order.
{47}Order V. PAUROPODA.
A pair of limbs to each segment. Antennae branched. Eyes few or none.
Labrum and labium indistinct. Genital orifice at the base of the second
pair of limbs. Free dorsal scutes. Nine pairs of feet (always?). Some
segments with sensitive hairs. Last segment the smallest.
Family 1. _Pauropidae._
Body slender. Dorsal scutes smooth. Limbs long and projecting from the
lateral margins of the body. Colour pale.
THE STRUCTURE OF THE MYRIAPODA.
Having now given a short view of the classification of the Class, I will
proceed to give a general account of their structure, the variations in
which have led to the divisions into the various Orders and Families. Their
structure shows resemblances to several widely different classes of
animals. One cannot help being impressed with their likeness to the Worms,
at the same time they have affinities with the Crustaceans, and still more
with the Insects. In the latter class the likeness of the Thysanuridae to
_Scolopendrella_ and _Pauropus_ have induced a celebrated Italian
anatomist, Professor Grassi, to claim the former as the ancestors of the
Myriapoda.
Myriapods have a body which is segmented, as it is termed; that is,
composed of a number of more or less similar parts or segments joined
together.
One of the most important characteristics which distinguish Myriapods from
other Arthropoda is the fact that they possess on the posterior segments of
the body true legs which are jointed and take part in locomotion. The head
is in all cases quite distinct from the body, and may be regarded as a
number of segments fused together into one mass. Their heads are always
provided with a single pair of _antennae_ and mouth appendages, consisting
of an upper lip, a pair of _mandibles_ or jaws, and one to two pairs of
_maxillae_. The mandibles resemble those of Insects, and are strongly
toothed. In the Chilognatha a pair of maxillae are fused so as to form a
single oval appendage. In the Chilopoda they each consist of a single blade
bearing a {48}short palp or feeler. The mouth parts may have the forms
known as chewing, biting, or suctorial (_Polyzonium_) mouth appendages.
With the exception of the terminal segment, and in many cases the first or
the seventh, each segment bears one or two pairs of limbs. These may be
very long, as in _Scutigera_, or very short, as in _Polyxenus_. They may be
attached close to one another near the ventral middle line of the body, or
may have their bases far apart from each other, as in the Chilopoda. The
exoskeleton or external armour is composed of chitin (Chilopoda) or of
chitin with calcareous salts deposited in it (Chilognatha).
Their internal structure has a great likeness to that of Insects.
The general position of the internal organs may be seen from Fig. 28, which
shows a _Lithobius_ dissected so as to exhibit the digestive and nervous
systems.
_The digestive canal_, which is a straight tube, extends throughout the
whole length of the body, and terminates in the last segment of the body.
It may be divided into the following parts:—
1. A narrow oesophagus, beginning with the mouth or buccal cavity, and
receiving the contents of two or more salivary glands (_d_).
2. A wide mesenteron or mid-gut (_n_) extending throughout almost the
whole length of the body.
3. A rectum which at its junction with the mid-gut receives the contents
of two or four _Malpighian tubes_ (_g_, _h_) which function as kidneys.
Their function was for a long time unknown, but the discovery of crystals
of uric acid in them placed the matter beyond doubt.
_The heart_ has the form of a long pulsating dorsal vessel which extends
through the whole length of the animal. It is divided into a number of
chambers, which are attached to the dorsal wall of the body, and are
furnished with muscles of a wing-like shape, which are known as the alary
muscles, and which govern its pulsations. The chambers are furnished with
valves and arteries for the exit of the blood, and slits known as _ostia_
for the return of the blood to the heart. The blood enters the chambers of
the heart from the body cavity through the {49}ostia, and passes out
through the arteries to circulate through the organs of the body and to
return by the ostia.
[Illustration: FIG. 28.—_Lithobius_ dissected. (After Vogt and Yung.) _a_,
antennae. _b_, poison claws. _c_, brain. _d_, salivary glands. _e_, legs.
_f_, nerve cord. _g_, Malpighian tube. _h_, Malpighian tube. _i_, vesicula
seminalis. _j_, accessory gland. _k_, accessory gland. _l_, testis. _m_,
thigh gland. _n_, digestive tube. ]
The two figures below (Figs. 29 and 30) show the position of the arteries
and the ostia in a single segment of the body. The heart is too small and
delicate to be seen with the naked eye; it therefore requires the aid of
the microscope. A freshly-killed animal was therefore taken and prepared in
the manner known to all microscopists, and extremely thin slices or
sections cut horizontally from its back. One of these sections cut the
whole length of the heart in one segment, which was accordingly drawn under
the microscope (Fig. 29), and shows a longitudinal {50}horizontal section
through the whole length of the heart in a single segment, with the two
ostia at each end of the segment and the two arteries in the middle.
The arteries, when they leave the body, pass into masses of fatty tissue on
either side of the heart, and the other figure (Fig. 30) is intended to
show the artery leaving the heart and penetrating into the fatty tissue.
The figure is taken from the same section as the former one, but is much
more highly magnified, so as to show more detail. The delicate coats of the
heart are shown, the artery being covered with a clothing of large cells.
[Illustration: FIG. 29.—Heart of _Julus terrestris_ showing ostia (_ost_)
and arteries (_Art_) magnified.]
[Illustration: FIG. 30.—Heart of _Julus terrestris_ showing structure of
artery (_Art._) and external coat of heart (_ext.c_), also fat body (_Fb_),
highly magnified. _Ht_, The cavity of the heart. The circular muscle fibres
which surrounds the heart are shown just below the external coat (_ext.c_).
_ogl_, Oil globules of the fat body.]
Myriapods breathe by means of _tracheae_, with the exception of the
Scutigeridae, which have an elementary form of lung which resembles that of
spiders, and will be mentioned further on. These tracheae, as in Insects,
are tubes lined with chitin, which is arranged in spiral bands. The
tracheae open to the exterior by openings called _stigmata_, through which
they receive the external air, which passes into the main tracheal tubes
and into their ramifications, and thus effects the aeration of the blood.
The _nervous system_ of the Myriapods consists, as in Insects, of a brain,
which may be more or less developed, a circumoesophageal ring embracing the
oesophagus, and a ventral chain of ganglia, and in some cases (Newport) of
a system of visceral {51}nerves. With the nervous system we may mention the
sense organs, the eyes, which are present in most cases, though wanting, as
has been already stated, in many groups. They are usually present as
clusters of ocelli or eye spots closely packed together, or (in
_Scutigera_) as peculiarly formed facetted eyes. The sensory hairs on the
antennae must be reckoned as sense organs, as also the tufts of sense hairs
on the head of _Polyxenus_. _Scutigera_ has also a peculiar sense organ
beneath the head, consisting of a sac opening on the under side of the head
full of slender hairs, each of which is connected at its base with a nerve
fibre. Except the eyes, the Myriapod sense organs have usually the form of
hairs or groups of hairs connected with nerve fibres, which communicate
with the central nervous system.
[Illustration: FIG. 31.—Under side of the head of _Scutigera coleoptrata_,
with sense organ. _eo_, Opening of sense organ to the exterior; _o_, sense
organ shown through the chitin; _m_, mouth; _oc_, eye; _mxl_, maxilla; _f_,
furrow in the chitin. (Heathcote, Sense organ in _Scutigera coleoptrata_.)]
[Illustration: FIG. 32.—Highly magnified section through head of _Polyxenus
lagurus_, showing sense organ. _ext.cut_, external cuticle; _t_, tube
surrounding base of sense hair; _gang.c_, ganglion cell. (Heathcote,
Anatomy of _Polyxenus lagurus_.)]
These two sense organs are shown in Figs. 31 and 32. Fig. 31 shows the
under side of the head of _Scutigera_ (Fig. 17), with the position of the
sense organ and its opening. Fig. 32 is part of a section through the head
of _Polyxenus_ with two of the sense hairs. Each spine or sense hair fits
into a cup in the chitin of the head; and the lower or internal part, which
is divided from the upper or external part by a rim, is joined to a
ganglionic nerve cell (_gang.c._).
The Myriapods are of separate sexes, and the generative organs in both
cases usually have the form of a long unpaired {52}tube, which in the male
is connected with accessory glands, and in the female is usually provided
with double receptacula seminis. The generative openings usually lie near
the base of the second pair of legs (Chilognatha), or at the posterior end
of the body (Chilopoda). In the Chilognatha there is usually in the male an
external copulatory organ at the base of the seventh pair of legs, remote
from the genital opening.
The preceding account of the anatomy of the Myriapods has shown us the
general characteristics of the whole group. I shall now take each of the
five Orders into which the class is divided in the classification adopted
in this account, and endeavour to explain the differences in anatomy which
have led to the establishment of the Order. The first Order with which we
have to do is that of the Chilognatha, which includes a large number of
Myriapods; no less than eight families, some of them including a great
number of forms.
ORDER I. CHILOGNATHA.
The Chilognatha differ from other Orders in the shape of the body. This is
in almost all cases, cylindrical or sub-cylindrical, instead of being more
or less flattened as in the other Orders.
The body, as in all other Myriapods, is composed of segments, but in the
Chilognatha these segments are composed, in almost all cases, of a complete
ring of the substance of which the exoskeleton (as the shell of the animal
is called) is composed. This substance is in the case of the Chilognatha
chitin (a kind of horny substance, resembling, for instance, the outer case
of a beetle's wing), containing a quantity of chalk salts and colouring
matter; the substance thus formed is hard and tough. In other Orders the
chitin of the exoskeleton is without chalky matter and is much more
flexible. The length of the body, as may be seen from the classification,
may be either very long, as in _Julus_, or very short, as in _Glomeris_.
The next anatomical character distinctive of the Order is the form of the
appendages. First, the antennae. These are, as a general rule, much shorter
than in the Chilopods, never reaching the length of half the body. They
are, as a rule, club-shaped, the terminal half being thicker than the half
adjoining the body.
{53}The next appendages to be mentioned are the _mouth parts_. These differ
in form from those of the other Orders, and their differences are connected
very largely with the fact that the Chilognatha live on vegetable
substances. Their mouth parts are adapted for chewing, except in the case
of the Polyzoniidae, the eighth family of the Order, in which, according to
Brandt, the mouth parts are adapted for sucking, and are prolonged into a
kind of proboscis. The mouth parts of the Chilognatha consist of—
(1) _An upper lip._ A transversely-placed plate, which is fused with the
rest of the head.
(2) A pair of powerful mandibles or jaws adapted for mastication, and
moved by powerful muscles. _f_ and _g_ in Fig. 33 shows these mandibles,
while the rest of the figure constitutes the broad plate (No. 3).
(3) A broad plate covering the under part of the head and partially
enclosing the mouth. This structure, which, as we shall afterwards see,
is formed by the fusion of two appendages which are distinct in the
animal when just hatched, has been called the deutomalae, the jaws
receiving the name of protomalae.
[Illustration: FIG. 33.—Mouth parts of _Chilognatha_. (From C. L. Koch,
_System der Myriapoden_.) _f_ and _g_, The mandibles. The parts marked _a_,
_b_, _c_, _d_, _e_ are firmly united and constitute the broad plate No. 3.
They have received the following names—_a_, _b_, Internal stipes; _c_,
external stipes; _d_, malellae; _e_, hypostoma.]