Chapter IV: Part 4

The tergal elements of the somites bearing the antennae, mandibles and
maxillae appear to be represented by the head-shield or cephalite. The
tergal element of the somite bearing the palpognath is usually
suppressed; that of the toxicognath is sometimes of large size as in
some Geophilomorpha (_Himantarium_), sometimes small as in
_Scutigera_, _Lithobius_, _Craterostigmus_, sometimes suppressed
probably by fusion with the tergum of the first leg-bearing somite as
in the Scolopendromorpha. The sternal plates of all the jaw-bearing
somites have disappeared, except in the case of the somite of the
toxicognath, where it may be vestigial. In the case of the somites
bearing the walking legs the tergal and sternal elements are preserved
without fusion with the corresponding plates of the preceding or
succeeding somites, so that great flexibility of the body is retained.
The only exception to this is presented by _Scutigera_, where the
terga corresponding to the somites bearing the fifteen pairs of legs
are reduced by fusion and suppression to seven. The walking legs are
articulated to the inferior portion of the pleural or lateral area of
the somites close to the external margins of the sterna, which widely
separate those of the left from those of the right side. Generally
speaking the legs resemble each other, although as a rule they
progressively increase in length towards the posterior end of the
body. They consist typically of six segments, of which the basal is
termed the coxa and the apical the tarsus. The tarsus is armed with a
single terminal claw, and, except in the Geophilomorpha and a few
genera of other orders, is divided by a mesial transverse joint into
two segments, as is the case in _Scolopendra_ and _Lithobius_ for
example. But in some of the longer-legged, swift-footed centipedes of
the order Lithobiomorpha (e.g. _Henicops_, _Cermalobius_) the tarsi
are further subdivided. The multiplication of sub-segments reaches its
maximum in _Scutigera_, where the tarsi are extremely long, slender,
flexible and annulated. The legs of the last pair are directed
backwards in a line parallel with the long axis of the body, so that
their coxae, fused in some cases with the pleural sclerites
(_Scolopendra_, _Geophilus_), or free and of large size (_Scutigera_,
_Lithobius_), serve to protect the small genital and anal somites.
They are often greatly modified. In the males of some species of
_Lithobius_ one or more of the segments is inflated or furnished with
tubercle-bearing, tactile bristles; in some Geophilomorpha the whole
limb is thickened in the male sex. In most Scolopendromorpha the basal
segment is armed beneath with spines or spikes (_Dacetum_,
_Scolopocryptops_); sometimes the whole appendage is thickened and
terminated by a sharp and serrate claw (_Theatops_, _Plutonium_). In
these cases the legs act as weapons of defence and offence. In other
cases (_Newportia_) the tarsi lose the claw, become many-jointed and
act as feelers, while in _Alipes_ the terminal segments are flattened,
leaf-like and furnished with a peculiar stridulating organ. The
genital somite is always small and sometimes retractile within the
somite bearing the last pair of legs. Its tergal plate is usually
retained, but its sternal plate is generally suppressed. In females of
the Lithobiomorpha and Scutigeromorpha the appendages of this
somite--the gonopods--are jointed, forcipate and relatively well
developed although small. In the females of the other orders they are
greatly reduced or absent. In the males their development varies
considerably. They are well developed in _Scutigera_, where they form
two pairs of digitiform sclerites, whereas in the Geophilomorpha they
are reduced to a pair of very short, two-jointed limbs. The anal
somite is always small and limbless. In _Craterostigmus_ the genital
and anal somites are represented by a pair of elongate valves
projecting between the legs of the last pair. The structure of the
gonopods is unknown, and the homology between the two valves and the
skeletal elements of the somites in question not clearly understood.

A study of the development of _Scolopendra_ has shown that the
antennae of the adult are the appendages of the second postoral
metamere and the mandibles those of the fourth, the first postoral
metamere, which has a pair of transient preantennal appendages, and
the third, which has no appendages, being excalated at an early stage
of embryonic growth. Furthermore, behind the legs of the last pair two
pairs of appendages are present. The second of these persists as the
gonopods of the adult, but the first is suppressed. Possibly, however,
it is represented in the male of _Scutigera_ by the anterior branches
of the gonopods. The cerebral or cephalic portion of the nervous
system consists of a quadrilobate mass. From the two upper lobes,
which are set transversely, arise the ocular nerves; from the two
lower lobes, which are united by a transverse commissure, spring the
antennal nerves in front and the chords which form the oesophageal
collar behind. These chords unite below the oesophagus to form the
compound suboesophageal ganglion, whence the nerves for the four pairs
of jaws arise. The ventral system consists of a double chord uniting
in each of the leg-bearing segments in a ganglionic swelling which
gives off four pairs of nerves to the limbs and tissues of the somite.
There is a single ganglion in the genital segment.

FIG. 1.

A, Diagram of anterior extremity of an early embryo of
_Scolopendra_, ventral view; cl, clypeus; lb, labrum; m, mouth; p.a,
preantennal appendage; a, antenna; int, premandibular rudiment; mdl,
mandible; mx, maxilla; p.g, palpognath; t.g, toxicognath; lg. 1,
first pair of walking legs.

B, Posterior end of a later embryo of _Scolopendra_, ventral view,
showing the anal segment or telson (t); the legs of the last pair in
the adult (lg. 21) and the two rudimentary pairs of legs (lg. 22,
lg. 23).]

Eyes are frequently absent. When present they may be either simple or
compound, i.e. consisting externally of a single lens (monomeniscous)
of or an aggregation of lenses (polymeniscous). Simple eyes vary in
number on each side of the head from one, as in _Henicops_, to many as
forty, as in some species of _Lithobius_. In _Scolopendra_, where
there are four, the corneal lens is a biconvex thickening of the
cuticle. The soft or retinal portion of the eye beneath the lens
consists of an aggregation of large cells forming a single layer
continuous with the epidermic cells of the circumocular area. Thus the
eye is monostichous. The arrangement of the cells, however, is
peculiar. They are invaginated to form what may be described as a very
deep cup with exceedingly thick walls and correspondingly narrow
median space, the outer surface of the cup being formed by the inner
or proximal ends of the cells and the inner surface by their outer or
distal ends. It results from this arrangement that the cells forming
all but the bottom of the invagination lie horizontally, i.e. at right
angles to the vertical axis of the eye. From the distal ends of the
cells are secreted chitinous rhabdomeres, forming a rhabdom which
occupies and fills up the central portion of the cup beneath the
middle of the corneal lens. The outer ends of the cells are nucleated
and are continuous with the fibres of the optic nerve, which passes
from the outer surface of the bottom of the cup to the brain. Compound
eyes are found only in the _Scutigeridae_. Externally the eye consists
of one hundred or more little lenses or lenticles. The retinal portion
is composed of a corresponding number of ocular units or ommatidia.
Each ommatidium is an elongated cone with its broad extremity abutting
against the corneal lenticle. It consists of a non-nucleated
crystalline cone developed from embryonic cells, and is enveloped in
three tiers of large nucleated cells. The cells of the outermost tier
are heavily pigmented; those of the middle and innermost (proximal)
tiers, the retinal cells, are at their inner extremities produced into
threads continuous with the fibres of the optic nerve. In the space
between these cells and the crystalline cone which they surround,
there is a layer of rhabdomeres deposited apparently by the cells.

C after Adensamer, _Verh. z. b. Verein_, Vienna, 1893, pl. vii.

FIG. 2.

A, Brain of _Scolopendra_. n.ant, Antennal nerves; n.opt, ocular
nerves; n.pr.ant, preantennal nerves; oes. comm, oesophageal
commissure.

B, Section of Eye of Scolopendra. len, Corneal lens; ret, retinal or
visual cells; n.opt, optic nerve.

C, Ocular unit or ommatidium of compound Eye of _Scutigera_. len,
corneal lenticle; c.c, crystalline cone; 1, pigmented cells of
outermost tier; 2, 3, retinular cells of middle and innermost tiers;
rbd, rhabdomeres; n.opt, optic nerve; pg, pigment cells.]

The alimentary canal is a simple tube running without convolutions
from the mouth to the anus. Its anterior portion or pharynx, which
arises from the stomodaeal invagination in the embryo, is short; a
pair of large, so-called salivary glands open into it. The mesenteric
part of the canal is relatively wide and receives at its junction with
the hind-gut the excretory products of a pair of very long and slender
malpighian tubes of proctodaeal origin. The posterior end of the
canal, arising from the proctodaeum, is relatively short and narrow.

a, Anus.

mg, Mid-Gut.

hg, Hind-Gut.

mt, Malphighian tubule.

s.gl, Salivary gland.

lg. 1, lg. 15, Legs of first and fifteenth pairs.]

The generative organs vary in structural details in different
centipedes. In the male of _Lithobius_ the testes consist of a single
coiled tube lying above the alimentary canal. The slender vas deferens
which proceeds from its hinder end divides posteriorly into a right
and left branch, embracing the gut and uniting beneath it to form a
common chamber or atrium within the genital orifice. The atrium
receives the secretion of two pairs of large accessory glands; and a
pair of tubes, or vesiculae seminales, open, one on each side, into
the divided sperm ducts close to their point of origin above the
intestine. The organs of the female are very similar. There is a large
median ovary followed by a short oviduct forming a circum-intestinal
collar and a common atrium. Into the latter open a pair of short
receptacula seminis and the slender duct of two pairs of large
accessory glands. There is nothing in the female corresponding to the
supra-intestinal vesiculae seminales of the male. In the male of
_Scolopendra_, on the contrary, there are as many as twelve pairs of
somewhat sausage-shaped testes, approximated two by two. From each
pair proceed two slender ducts which open into a median duct coiled in
the posterior third of the body and much expanded in the last three of
the leg-bearing segments. The right and left portions of the
intestinal ring of the genital duct are unequally developed, and there
are no vesiculae seminales, but two pairs of accessory glands
communicate with the genital atrium as in _Lithobius_. In the female
_Scolopendra_ the right and left portions of the intestinal collar are
also unequally developed, and only a single pair of accessory glands
besides the receptacula seminis open into the atrium.

FIG. 4.--Posterior portion of generative organs of male of
_Scolopendra_ (A), of female (B). t, Testes; v.d, vas deferens; ov,
ovary; _r.s_, receptaculum seminis; gl. acc, accessory glands; g.o,
generative orifice.]

The heart is tubular and lies in the middle dorsal line immediately
beneath the integument. It consists of a series of chambers
corresponding roughly to the leg-bearing segments, and lies in a
blood-sinus formed by a pericardial membrane whence large alary
muscles extend to the sides of the body. Each chamber gives off in
_Scolopendra_ a pair of fine lateral vessels, and is furnished at its
posterior extremity with a pair of orifices by which the blood
re-enters the organ from the pericardial space. From the anterior
chamber, which lies in the first or second leg-bearing segment,
proceed three arteries, a median which runs forwards into the head to
supply the brain and other organs, and a lateral which with its fellow
of the opposite side forms an oesophageal aortic collar. From the
sides of the latter arise vessels to the gnathites, and from its
inferior portion an unpaired vessel passes forwards into the head and
another backwards above the nerve chord to the posterior end of the
body, supplying each segment in its course with a delicate lateral
branch. In _Scolopendra_ the chambers of the heart, excepting the
first and last, which are small, are subequal in size; but in forms
like _Scutigera_ where the terga are very unequal in size a
corresponding inequality in the size of the chambers is manifested.

FIG. 5.

A, Anterior extremity of _Scolopendra_, showing two chambers of the
heart (h), the aortic ring (a), the alae cordis (a.m) and a cardiac
orifice (o).

B, Two segments of _Scolopendra_, showing the branching and
anastomosing tracheae and a spiracle (sp).

C, A pair of tufted tracheae of _Scutigera_. d, Dorsal plate; t.s,
tracheal sac; tr, tracheal tubes.]

In all centipedes, except _Scutigera_, respiration is effected by
chitinized tracheal tubes which extend with their ramifications
throughout the body and open to the exterior by means of spiracles
perforating the lateral or pleural membrane of more or fewer of the
somites below the edge of the terga. Spiracles are never present upon
the anal, genital and last leg-bearing somites, and only rarely, as in
_Henicops_, upon the somite bearing the legs of the first pair. In the
majority of cases the spiracles are circular, sigmoid or slit-like
orifices, with chitinized rim, leading into a pocket-like integumental
infolding, from which emanate numerous small tracheal tubes which soon
anastomose to form the main tracheal trunks. In _Dacetum_, one of the
_Scolopendridae_, there is no pocket-like infolding, the small
tracheal tubes opening direct to the exterior on a large subcircular
plate where their apertures fuse to form a complicated network. The
apertures, as in the case of other genera, are protected by fine
hairs; and the tracheae themselves are strengthened by a fine spiral
filament. In the _Lithobiidae_ the tracheae do not anastomose; but in
_Scolopendra_ and _Geophilus_ the main trunks in each segment fuse
transversely with those of the opposite side and also longitudinally
with those of the preceding and succeeding segments.

In _Scutigera_ the tracheae differ both in structure and position from
those of all other Chilopoda. The spiracles, unpaired and seven in
number, open in the median dorsal line. Each leads into a short sac
from which five tracheal tubes depend into the pericardial
blood-sinus.

Existing Chilopoda may be classified as follows, into five orders
referable to two subclasses--

Subclass I. Pleurostigma.
Order 1 Geophilomorpha.
Order 2 Scolopendromorpha.
Order 3 Craterostigmomorpha.
Order 4 Lithobiomorpha.

Subclass II. Notostigma.
Order 5 Scutigeromorpha.

SUBCLASS I, PLEUROSTIGMA.--Chilopods furnished with a rich system of branching tracheal tubes, the spiracles of which are paired and open upon the pleural area of more or fewer of the somites. Each leg-bearing somite contains a distinct tergum and sternum, the number of sterna never exceeding that of the terga. Eyes are either preserved or lost; when preserved they are represented either by a single one-lensed ocellus or by an aggregation of such ocelli on each side of the head. The anterior portion of the head, bearing the labrum, is bent sharply downwards and backwards beneath the larger posterior portion lying behind the antennae, so that these appendages, approximated in the middle line, project directly forwards from the margin of the head formed by this retroversion of the labral area. The maxillae are short and have no sensory organ; the palpognaths consist of four segments, and the toxicognaths have their basal segments fused to form a single coxal plate.

_Order 1. Geophilomorpha_.--Chilopods with a large and indefinite
number of somites, most of which are partially or completely divided
into a smaller anterior segment, represented by a pretergal and two
presternal sclerites, and a larger posterior segment bearing the
spiracles and legs. Spiracles are present upon all the leg-bearing
somites except the first and last; and the legs which are short and
subequal in length consist of six segments, the basal of which remains
small. There are no eyes, and the antennae consist invariably of
fourteen segments. The tergal plate of the somite bearing the
toxicognaths always remains distinct and separates the head-shield
from the tergum of the first leg-bearing somite. The penultimate and
antepenultimate segments of the toxicognaths are reduced on the
preaxial side of the appendage to the condition of arthrodial
integumental folds and suppressed on the postaxial side where the
distal segment or fang is firmly jointed to the femoral segment. In
the last leg-bearing somite the pleural sclerites coalesce with the
coxa of the appendage; but the second segment (trochanter) of this
appendage does not fuse with the third (femur). The genital and anal
somites are not retractile within the last leg-bearing somite, and the
gonopods typically persist in the male as small two-jointed appendages
and in the female as jointed or unjointed sclerites. The young are
hatched with the full number of segments.

A, Upper view of anterior extremity in _Geophilus_.

a, Basal segments of antennae.

c, Cephalic plate.

t.palp, Tergal plate of somite, bearing palpognaths.

t.tox, Tergal plate of somite, bearing toxicognaths (_tox_).

t.lg.1, Tergal plate of somite, bearing legs of first pair.

B, Toxicognaths of _Scolopendra_, showing the large coxal plate and
the reduced penultimate and antepenultimate segments.

C, Terminal segment or fang of the same, showing the orifice of the
poison gland.]

_Remarks._--The Geophilomorpha are universally distributed in suitable
localities. The number of families into which the order should be
divided is as yet unsettled, some authors admitting several groups of
this rank, others referring all the genera to a single family,
_Geophilidae_. In habits the _Geophilidae_ are mostly subterranean,
living in the earth and feeding principally upon earthworms.
Occasionally they may be found eating fruit or fungi, probably for the
sake of moisture. Although without eyes, they are extremely sensitive
to light, and when exposed to it crawl away in serpentine fashion to
the nearest sheltered spot, feeling the way with their antennae. They
can, however, progress with almost equal facility backwards, using
the legs of the posterior pair as feelers. Differing from the majority
of the family in habits are the two species _Linotaenia maritima_ and
_Schendyla submarina_, which live under stones or seaweed between
tide-marks on the coasts of western Europe. Most, if not all, the
species are provided with glands, which open upon the sterna and
secrete a fluid which in some forms (_Himantarium_) is blood-red,
while in others it is phosphorescent. In the tropical form _Orphnaeus
phosphoreus_ the fluid is known to possess this property; and its
luminosity has been repeatedly observed in England in the autumn in
the case of _Linotaenia acuminata_ and _L. crassipes_.

The number of pairs of legs within this family varies from between
thirty and forty to over one hundred and seventy. Corresponding
discrepancies are observable in size, the smallest specimens being
less than 1 in. long and barely 1 mm. wide, while the largest example
recorded, a specimen of _Notiphilides_ from Venezuela, was 11 in. long
and 1/3 of an inch wide.

When pairing takes place the female fertilizes herself by taking up a
spermatophore which a male has left upon a sheet of web for that
purpose. The female lays a cluster of eggs in some sheltered spot,
sometimes in a specially prepared nest, and encircling them with her
body, keeps guard until the young disperse and shift for themselves.

A, a, Cephalic plate.

b, Tergum of segment, bearing first pair of legs (d).

c, Tip of palpognath.

e, Antenna.

f, Toxicognath.

g, Last pair of appendages, enlarged and directed backwards.]

_Order 2. Scolopendromorpha._--Chilopods differing principally from
the Geophilomorpha in that the number of leg-bearing somites is
definitely fixed at twenty-three or twenty-one. These are
differentiated into larger and smaller, which alternate with nearly
complete regularity. The anterior portion of each somite is only
partially cut off as a subsegment. The tergal plate of the somite
bearing the toxicognaths is suppressed, probably by fusion with the
tergum of the first leg-bearing somite. The antennae consist of a
number of segments varying from seventeen to about thirty, and usually
differing in the individuals of a species. The second segment
(trochanter) of the legs of the last pair is coalesced with the third
(femur). In only one genus, namely _Plutonium_, which occurs in Italy,
is there a pair of spiracles for each leg-bearing segment, except the
first and last, as in the Geophilomorpha. In most genera there are
only nine pairs of spiracles situated upon the 3rd, 5th, 8th, 10th,
12th, 14th, 16th, 18th and 20th leg-bearing segments, as in
_Scolopendra_, _Cormocephalus_, _Cryptops_, &c. In genera with
twenty-three pairs of legs, like _Scolopocryptops_, there is an
additional pair of spiracles on the twenty-second pedigerous segment;
and a few genera such as _Rhysida, Edentistoma_, possess a pair upon
the 7th segment. Eyes, when present, are always four in number on each
side. The newly hatched young has the full complement of appendages.

This order is divided into four families:--_Scolopendridae_
(_Scolopendra_, _Rhysida_), _Cryptopidae_ (_Cryptops_, _Theatops_),
_Scolopocryptopidae_ (_Scolopocryptops_, _Otocryptops_) and
_Newportudae_ (_Newportia_). Apart from the frigid zones it is
cosmopolitan in distribution, though only one genus (_Cryptops_)
extends into north temperate latitudes. In the tropics and warmer
countries of the southern hemisphere the genera and species are
particularly abundant, and individuals reach the greatest dimensions,
some specimens of the tropical American species _Scolopendra gigantea_
exceeding 12 in. in length. They are strictly carnivorous, their diet
consisting of any animal, vertebrate or invertebrate, small enough to
be overcome. They live in damp obscure places, under logs of wood or
stones, and are nocturnal, shunning, like the _Geophilidae_, exposure
to light; and as in the _Geophilidae_, the females guard their eggs
and young until the latter disperse to lead an independent life.

_Order 3. Craterostigmomorpha_.--Chilopods with twenty-one tergal
plates as in the typical genera of Scolopendromorpha, but with only
fifteen pairs of legs as in the Lithobiomorpha. As in some members of
the latter order there is a single ocellus on each side of the head,
the penultimate and antepenultimate segments of the toxicognaths are
complete on the postaxial side of the appendage, and spiracles are
present upon the 3rd, 5th, 8th, 10th, 12th and 14th leg-bearing
somites. In the size and shape of the head, of the toxicognaths, of
the tergal plate of this somite, and of the first leg-bearing somite,
great similarity to some genera of Geophilomorpha (e.g.
_Mecistocephalus_) is presented; but in the structure of the posterior
end of the body this order differs from all the other orders of
Chilopoda. The skeletal elements of the last leg-bearing segment are
welded together to form a subcylindrical tube, and the genital and
anal somites are represented by a pair of chitinous valves capable of
opening below for the escape of the genital and intestinal products.

FIG. 8.

A, Anterior end of _Craterostigmus_ from above.

a, Basal segments of antennae.

c, Cephalic plate with eyes (o).

t.tox, Tergal plate of somite bearing toxicognaths (tox).

t.lg.1, Tergal plate of somite bearing legs of the first pair.

B, Maxillae.

C, Palpognath.

D, Toxicognath.

E, Last segment with genital capsule (g.c), and basal segments of
legs of 14th and 15th pairs (lg. 14, lg. 15).]

This order, containing the family _Craterostigmidae_, is based upon a
remarkable genus and species _Craterostigmus tasmanianus_, of which
only two specimens are known. These were collected under stones upon
the summit of Mount Rumney in Tasmania. They are about 1½ in. in
length; but nothing has been recorded of their habits. The chief
morphological interest attaching to _Craterostigmus_ is that, apart
from certain structural peculiarities of its own, it presents features
previously believed to be found exclusively either in the
Scolopendromorpha, or the Geophilomorpha, or the Lithobiomorpha; and
it shows how the Lithobiomorpha may be derived from a
Scolopendromorphous type most nearly resembling _Plutonium_ by the
excalation of the third, sixth, ninth, eleventh, fourteenth and
seventeenth leg-bearing somites.

_Order 4. Lithobiomorpha._ Chilopoda with fifteen pairs of leg-bearing
somites differentiated into larger and smaller, the 1st, 3rd, 5th,
7th, 8th, 10th, 12th and 14th being large, the others small. Spiracles
present upon all the larger with the exception sometimes of the 1st.
The toxicognaths are relatively weaker than in the orders hitherto
considered, and have their basal segments less firmly fused mesially.
In correlation with their weaker muscularity the first leg-bearing
segment is relatively small. The gonopods, present and usually jointed
in both sexes, are especially well developed and forcipate in the
female, and arise from a large ventral plate resulting from the fusion
of their coxae with the sternum of the genital somite. The antennae
are many-jointed, and there is a single ocellus or a cluster of ocelli
on each side of the head. The coxae of the legs are large, and those
of the last four or five pairs usually contain glands opening by large
orifices. The newly-hatched young has only seven pairs of legs, the
remaining pairs being successively added as growth proceeds.

The genera of this order are divisible into three families, the
_Lithobiidae_ (_Lithobius, Bothropolys_), _Henicopidae_ (_Henicops,
Haasiella_), the _Cermatobiidae_ (_Cermatobius_). _Cermatobius_, based
upon a single species, _martensii_, from the isl. of Adenara, is of
peculiar interest, since in the absence of coxal pores, and the length
and multi-articulation of the antennae and tarsal segments, it
approaches more nearly to _Scutigera_ than does any other
pleurostigmous Chilopod. It is also stated that the spiracles have
assumed a more dorsal position, thus foreshadowing the completely
dorsal situation they have taken up in the Notostigma. The
_Henicopidae_, containing centipedes of small size, attains its
maximum of development in the southern continents and islands, more
particularly Australia, New Zealand, South Africa and South America.
One genus (_Lamyctes_) however, occurs in Europe. The _Lithobiidae_,
on the contrary, are almost exclusively northern in range, being
particularly abundant and of large size individually in Europe,
extra-tropical Asia, and North and Central America. In habits the
_Lithobiidae_ closely resemble the _Scolopendridae_. They are,
however, comparatively far more agile with their shorter, more compact
bodies and stronger legs. They are mostly of small size, the largest
species, _Lithobius fusciatus_, of south Europe measuring only 2 in.
in length of body. The females do not guard their eggs, but coat them
with soil and leave them to their fate.

SUBCLASS 2, NOTOSTIGMA.--Chilopods with a series of median dorsal tracheal sacs furnished with tubes dipping into the pericardial blood space, and opening each by an unpaired spiracle upon the 1st, 3rd, 5th, 8th, 10th, 12th and 14th leg-bearing somites. This characteristic is accompanied by the complete disappearance of the tergum of the 7th, either by fusion with that of the 8th or by excalation, and by the evanescence of the terga of the 2nd, 4th, 6th, 9th, 11th and 13th pedigerous somites. The preantennal area of the head is not strongly reflexed inferiorly, and the eyes are large and compound. The maxillae are long and have a sensory organ, the palpognaths are long, spiny and composed of five segments, like the primitive Chilopod leg, and the toxicognaths have their basal segments disunited and independently movable. Gonopods duplicated in the male.

This subclass contains the single order Scutigeromorpha and the family
_Scutigeridae_. As in the Lithobiomorpha there are fifteen pairs of
legs, the gonopods are well developed in both sexes and the young is
hatched with only seven pairs of legs. The legs and antennae in the
adult are extremely long and many jointed. In habits as well as in
structure the _Scutigeridae_, of which _Scutigera_ is the best-known
genus, differ greatly from other centipedes. Although they hide under
stones and logs of wood like _Lithobius_, they are not lucifugous but
diurnal, and may be seen chasing their foes in the blazing sun. They
run with astonishing speed and have the power of dropping their legs
when seized. South of about the 40th parallel of north latitude they
are universally distributed in suitable localities. In most species
the body only reaches a length of about 1 in.; but twice that size or
more is reached by examples of the Indian species _Scutigera
longicornis_.

FIG. 10.--Gnathites of _Scutigera_.

I. Mandibles.
II. Maxillae.
III. Palpognaths.
IV. Toxicognaths.]

Some fossils of Carboniferous age have been described as Chilopoda by
Scudder, who refers them to two families, _Gerascutigeridae_ and
_Eoscolopendridae_. But until the specimens have been examined by
zoologists the genera they are alleged to represent cannot be taken
seriously into consideration. Remains of centipedes closely related to
existing forms have been recorded from Oligocene beds. (R. I. P.)

CENTLIVRE, SUSANNA (c. 1667-1723), English dramatic writer and actress, was born about 1667, probably in Ireland, whither her father, a Lincolnshire gentleman named Freeman, had been forced to flee at the Restoration on account of his political sympathies. When sixteen she married the nephew of Sir Stephen Fox, and on his death within a year she married an officer named Carroll, who was killed in a duel. Left in poverty, she began to support herself, writing for the stage, and some of her early plays are signed S. Carroll. In 1706 she married Joseph Centlivre, chief cook to Queen Anne, who survived her. Her first play was a tragedy, _The Perjured Husband_ (1700), and she herself appeared for the first time at Bath in her comedy _Love at a Venture_ (1706). Among her most successful comedies are--_The Gamester_ (1705); _The Busy Body_ (1709); _A Bold Stroke for a Wife_ (1718); _The Basset-table_ (1706); and _The Wonder! a Woman keeps a Secret_ (1714), in which, as the jealous husband, Garrick found one of his best parts. Her plots, verging on the farcical, were always ingenious and amusing, though coarse after the fashion of the time, and the dialogue fluent. She never seems to have acted in London, but she was a friend of Rowe, Farquhar and Steele. Mrs Centlivre died on the 1st of December 1723. Her dramatic works were published, with a biography, in 1761 (reprinted 1872).

CENTO, a town of Emilia, Italy, in the province of Ferrara, 18 m. S.E. direct from the town of Ferrara; 50 ft. above sea-level; it is reached by road (6 m. to the W.) from the station of S. Pietro in Casale, 15 m. S.W. by W. of Ferrara, and also by a steam tramway (18 m. N.) from Bologna to Pieve di Cento, on the opposite bank of the Reno. Pop. (1901) 4307 (town), 19,078 (commune). It is connected by a navigable canal with Ferrara. It was the birthplace of the painter Giovanni Francesco Barbieri (Guercino). The communal picture-gallery and several churches contain works by him, but none of first-rate importance. A statue of him stands in front of the 16th century Palazzo Governativo. The town was surrounded by walls, the gates of which are preserved. The origin of the name is uncertain.

CENTO (Gr. _[Greek: kentrôn]_, Lat. _cento_, patchwork), a composition made up by collecting passages from various works. The Byzantine Greeks manufactured several out of the poems of Homer, among which may be mentioned the life of Christ by the famous empress Eudoxia, and a version of the Biblical history of Eden and the Fall. The Romans of the later empire and the monks of the middle ages were fond of constructing poems out of the verse of Virgil. Such were the _Cento Nuptialis_ of Ausonius, the sketch of Biblical history which was compiled in the 4th century by Proba Falconia, wife of a Roman proconsul, and the hymns in honour of St Quirinus taken from Virgil and Horace by Metellus, a monk of Tegernsee, in the latter half of the 12th century. Specimens may be found in the work of Aldus Manutius (Venice, 1504; Frankfort, 1541, 1544). In 1535 Laelius Capitulus produced from Virgil an attack upon the dissolute lives of the monks; in 1536 there appeared at Venice a _Petrarca Spirituale_; and in 1634 Alexander Ross (a Scotsman, and one of the chaplains of Charles I.) published a _Virgilius Evangelizans, seu Historia Domini nostri Jesu Christi Virgilianis verbis et versibus descripta_.

CENTRAL AMERICA, that portion of the American continent which lies between Mexico and Colombia, comprising the British crown colony of British Honduras, and the six independent republics of Guatemala, Salvador, Honduras, Nicaragua, Costa Rica and Panama. These seven divisions are described in separate articles. Central America is bounded towards the N. by the Caribbean Sea, and towards the S. by the Pacific Ocean, and extends between 7° 12' and 18° 3' N. and between 77° 12' and 92° 17' W. It has an area of about 208,500 sq. m., and stretches for some 1300 m. from N.W. to S.E., in a succession of three serpentine curves, reaching its greatest breadth, 450 m., between the Peninsula of Nicoya and the north coast of Honduras, and diminishing to 35 m. in the Isthmus of Panama. The eastern boundary of Central America was usually regarded as identical with that of Costa Rica until 1903, when the republic of Panama was formed out of the northern territories of Colombia; and the more modern definition given above does not command the universal assent of geographers, because it fails to include the whole region up to the natural frontier on the north-west, i.e. the Isthmus of Tehuantepec in Mexico. It has, however, the support of political and historical considerations, as well as of common usage; and it may therefore be regarded as adequate, although, in respect of climate and natural products, it would be more accurate to define Central America as lying between Tehuantepec and Darien.

_Physical Features._--The _Cordilleras_, or mountain chains of Central
America do not form a complete link between the western ranges in the
north and south of the continent, for their continuity is interrupted
by various depressions, of which the chief is the lacustrine basin of
Nicaragua. With these exceptions, they traverse Central America from
end to end, their main axis trending from north-west to south-east.
They do not, as a rule, rise in sharply serrated ridges or series of
volcanic crests, like the Andes, but the central Cordilleras are
disposed in a succession of mountain masses, with many lesser chains
radiating from them. The principal summits have an altitude of 12,000
and even, in a few cases, of 13,000 ft., and the general character of
the ranges is volcanic, many craters being still active. Large tracts
of land remained imperfectly surveyed at the beginning of the 20th
century, owing to the unhealthiness of the tropical climate, and the
dense underwoods which impede exploration. In the northern part of
Guatemala, on the Pacific coast of the same country, in British
Honduras, along the Segovia river, on the Mosquito Coast, and in the
basin of Lake Nicaragua and the San Juan river, there are broad
stretches of comparatively flat country. The main line of watershed is
everywhere nearer to the Pacific than to the Atlantic, except in
southern Costa Rica and Panama, where it is almost equidistant from
the two oceans. In consequence, the rivers of the Pacific seaboard are
mostly short and swift,--mere mountain torrents, in many instances,
until they reach the sands and swamps which border the sea. The rivers
of the Atlantic littoral descend more gradually, and by longer
channels. The largest of them is the Segovia, in Nicaragua and
Honduras, which has a course of 450 m. Lake Nicaragua, the largest
inland sheet of water, has an area exceeding 3500 sq. m. There are
also several mountain lakes of exceptional interest and beauty, such
as Atitlán and Amatitlán, in Guatemala, besides two great land-locked
salt-water lakes--the Pearl Lagoon of the Mosquito Coast, and the
Carataska Lagoon in Honduras.

_Geology._--The neck of land which unites the continents of North and
South America is not, geologically, the direct continuation of either,
but constitutes a third element which is wedged, as it were, between
the other two. The folds in the earth's crust which form the Andes and
the Western ranges of North America, are not continued along the
connecting isthmus, where, on the contrary, the strata are folded from
west to east, obliquely across the trend of the continent. It should,
however, be noticed that the Andes, as they approach the Caribbean
sea, bend round towards the east; and it is probable that the folds of
the North American Cordillera similarly bend eastward beneath the
volcanic rocks of Mexico. The folds of Central America are tangential
to the two arcs thus formed.

By far the greater part of Central America and Mexico is covered by
Cretaceous and Tertiary deposits, both sedimentary and volcanic; but
the foundation on which they rest is exposed at intervals. From the
Rio Grande to the southern declivity of the Mexican plateau the
existence of ancient crystalline rocks at the surface is yet unproved,
but they probably occur in the Sierra Madre del Pacifico. South of the
plateau, in the state of Oaxaca, low mountain ridges composed of
granites and gneisses, supposed to be of Archaean age, begin to
appear. They strike from west to east, and mark the front of the
series of east and west folds which stand _en échelon_ across the
Central American region. Between the 15th and 17th parallels of
latitude, in the state of Chiapas and in the republic of Guatemala,
there is a second group of ridges composed of granites and schists
with an eastward trend. In this case the evidence of age is clear, for
the rocks are covered by a limestone which is proved to be
Pre-Carboniferous. Similar rocks, supposed to be of Archaean or at
least of early Palaeozoic age, occupy considerable areas in British
Honduras, Honduras and northern Nicaragua, and occur also in Costa
Rica and perhaps in Panama; and wherever the strike has been observed,
it is approximately from west to east. The presence of Palaeozoic
rocks has been proved in Guatemala and the adjacent state of Chiapas,
where limestones have been found containing many unmistakable
Carboniferous fossils, and below these is a considerable thickness of
beds supposed to be Silurian. Nowhere else in the Central American
region is there any palaeontological evidence of Palaeozoic rocks.

The Mesozoic series begins with sands and red or yellow clays
containing plant remains and possibly of Triassic age; but the
occurrence of these deposits is limited to a few small isolated
outcrops. Jurassic beds have been found in Mexico but not in Central
America. The Cretaceous system, consisting of a lower series of clays,
sandstones and conglomerates, followed conformably by an upper series
of limestones, covers a considerable area in Chiapas, Guatemala and
Honduras, and is found also in Costa Rica. The upper series contains
hippurites. The greater part of the eastern half of the Mexican
plateau is also formed of Cretaceous beds.

The Tertiary system may be conveniently divided into two divisions.
The lower, of Eocene and Oligocene age, consists generally of sand and
clays which were evidently laid down near a shore line. The upper
division also, including the Pliocene and Pleistocene (which have not
yet been clearly distinguished from each other), is usually of shallow
water origin; but in the northern part of Yucatan it includes beds of
chalky limestone, like those of the Antilles, which may have been
deposited in a deeper sea.

It is probable that folding took place at more than one geological
epoch, and the whole series of beds up to the Oligocene is involved in
the folds. The Pliocene, on the other hand, is usually undisturbed,
and the final effort must, therefore, have occurred during the Miocene
period, which appears to have been a period of great earth movement
throughout the Caribbean region. From the southern extremity of the
Mexican plateau to the Colombian border, the strike of the folds--of
the Mesozoic and early Tertiary deposits, as well as of the older
rocks--is in general from east to west; but there is one considerable
exception. On both sides of the deep depression which crosses Honduras
from Puerto Cortez to the Gulf of Fonseca, the strike is commonly from
north to south. The depression is probably a "Graben" or trough formed
by faulting.

The great volcanoes of Mexico and Central America stand upon the
Pacific side of the continent, and it is only where the land contracts
to a narrow neck that their products spread over to the Caribbean
shore. The extent of the volcanic deposits is very great, and over a
wide area they entirely conceal the original structural features of
the country. The eruptions began towards the close of the Cretaceous
period and continue to the present day. The rocks are lavas and ashes,
chiefly of andesitic or basaltic composition, but rhyolites and
trachytes also occur, and phonolite has been met with in one or two
places.

According to R.T. Hill, there is but little geological evidence of any
Tertiary or later connexion between the Caribbean Sea and the Pacific,
excepting, perhaps, a shallow opening during the Eocene period. It
should, however, be stated that all authorities are not agreed upon
this point, and K. Sapper found marls and sandstones which he believes
to belong to the Upper Tertiary, lying horizontally at a height of
about 7500 ft. in the Mexican state of Chiapas. Unfortunately the
fossils obtained from these beds were lost.

_Climate_.--The climate of Central America is subject to the most
marked local differences of heat and cold, owing partly to the
proximity of two oceans, partly to the variations of altitude which
render such territories as the swamps of the coast, or the lowlands of
British Honduras and northern Guatemala, totally unlike the alpine
regions of Salvador and Costa Rica. The whole area may, however, be
roughly divided into a tropical zone (_tierra caliente_), from
sea-level to about 1500 ft.; a temperate zone (_tierra templada_),
from 1500 to 5000 ft.; and a cold zone (_tierra fria_), above 5000 ft.
These figures are, of course, only approximately correct; and it often
happens that, at the same elevation, the heat is greater on the
Pacific than on the Atlantic versant. The rainy season on the Pacific
slope varies in duration from four to six months, between April and
December. It lengthens as the altitude increases. On the coast, it
corresponds with the prevalence of the south-west monsoon, the
tempestuous _Cordonazo de San Francisco_, or "Flagellation of St
Francis," as it is called in Mexico, and it is often interrupted by an
interval of two or three weeks of fine weather, known as the
_Veranillo de San Juan_, or "Little summer of St John." In the rainy
season, the morning has usually a clear sky; about two or three
o'clock in the afternoon the clouds begin to gather in great cumulus
masses; suddenly the lightning flashes out and the rain crashes down;
and by evening the sky is clear and starry. North winds are most usual
during the dry season. On the Atlantic coast the trade-winds may bring
rain in any month, and, owing to the moist atmosphere, the heat is
more oppressive. The rainfall may vary in successive years from less
than 50 in. to nearly 200 in., owing to the occurrence of
cloud-bursts. Frosts are not rare above 7000 ft., but snow seldom
falls.

_Fauna_.--The fauna of Central America is more closely connected with
the fauna of South than with that of North America. As the region is
comparatively small, and its limits conventional, there are
comparatively few species that it can claim as peculiarly its own. It
is almost entirely free from the presence of animals dangerous to man.
Of felines it possesses the jaguar (_Felis onza_), popularly called
the tiger; the cuguar (_Felis concolor_), popularly called the lion;
the tigrillo (_Felis tigrina_), which is sometimes kept tame; and
other species. Several species of monkeys (_Mycetes_ and _Ateles_) are
numerous in the warm coast region. The Mexican deer (_Cervus
mexicanus_) has a wide range both in the lowlands and highlands.
Besides the tapir there are several varieties of wild pig, such as the
marrano de monte (_Sus torquatus_) and the jabali or javali (_Sus
labiatus javali_). The _Edentata_ are represented by a species of
armadillo, the honey-bear (_Myrmecophaga tomandua_), and the
_Myrmecophaga didactyla;_ and among the rodents may be mentioned,
besides rats, hares and rabbits, the fruit-eating cotorra and
tepes-cuinte (_Dasyprocta aguti_ and _Coelogenys paca_), and the
troublesome _Geomys mexicana._ The manatee is common in all the larger
streams. Much annoyance is caused to the agriculturist by the little
marsupial called the tacuacine, or the _Didelphys carcinora,_ its
allied species. The bats are so numerous that villages have sometimes
had to be left to their undisputed occupancy. In the south-east of
Costa Rica the inhabitants are at times compelled to withdraw, with
all their live-stock, before the swarms of large migratory vampires
which in a single night can bleed the strongest animal to death. Most
of the domestic animals--the horse, ox, goat, sheep, pig, dog, rabbit,
common fowl, peacock and pigeon--are of European origin, and are
popularly grouped together as _animales de Castilla._ For the bird
collector there is a rich harvest. The catalogue of the National
Museum at Washington shows that Costa Rica alone possesses more than
twice as many species of birds as the whole of Europe. Among birds of
prey it is sufficient to mention _Corogyps atratus,_ the commonest of
the vultures, which acts as a universal scavenger, the _Cathartes
aura,_ the beautiful _Polyborus vulgaris,_ and the king of the
vultures (_Sarcorhamphus papa_). Neither the condor of the southern
continent nor the great eagles of the northern are known. The parrot,
macaw and toucan are found in all parts; the crow, blackbird, Mexican
jay, ricebird, swallow, rainbird, wood-pecker, humming-bird and trogon
are also widely distributed. A bird of the last-named genus, the
quetzal, quijal or quesal (_Trogon resplendens_) is of special note,
not only from the fact that its yellow tail-feathers. 2 or 3 ft. long,
were formerly worn as insignia by the Indian princes, but because it
has been adopted as the emblematical figure on the national arms of
Guatemala. The gallinaceous order is well represented, and comprises
several peculiar species, as the pavo de cacho, and the Peten turkey
(_Meleagris ocellata_), which has a bronze sheen on its plumage; and
aquatic birds, it is almost needless to add, are unusually numerous in
a region so richly furnished with lagoons, rivers and lakes.

Besides the alligator, which swarms in many rivers, the almost endless
varieties of Central American reptiles include the harmless boba or
chicken-snake, python and black snake; the venomous corali, taboba,
culebra de sangre and rattlesnake; iguanas of great size, scorpions,
edible lizards and other lizards said to be poisonous. In the rivers
and lakes, as in both seas, fish of many kinds abound; turtles and
tortoises are exported; and there are valuable pearl and oyster
fisheries. Insect life is even richer and more varied. Of the
_Coleoptera_, the Camelicorns, the Longicorns, the Curculionids, and
the Chrysomelines are said to be best represented, and of the
_Lepidoptera_ the prevalent genera are--_Ageronia, Papilio, Heliconia,
Sphinx_ and _Bombyx_. There are five species of bees, and the European
honey-bee, known as _aveja de Castilla_ or "bee of Castile," has been
naturalized. Ants are common, and may sometimes be seen marching in a
column 3 or 4 m. long. The mosquito, wood-tick, flea and locust are
unfortunately no less plentiful in certain districts, but their
distribution varies greatly, the mosquito being almost unknown in
parts of Honduras. A curious species of butterfly is the _Timetes
Chiron,_ which migrates in countless multitudes from the forests of
Honduras to the Mosquito Coast, but is never known to return.

_Flora_.--The flora of Central America ranges from the alpine to the
tropical, with the transition from one climatic zone to another.
Although its forest growths are, on the whole, inferior in size to
those of corresponding latitudes in the eastern hemisphere, it is
unsurpassed for beauty, luxuriance and variety. In the volcanic
districts, the soil is extremely fertile, yielding, where cultivated
and irrigated, magnificent crops of sugar, cotton, rice, tobacco,
coffee, cocoa and maize. Indigo is produced in small quantities; sugar
yields two or three crops, and maize as many as four, this cereal
supplying a chief staple of food. Plantains, bananas, beans, tomatoes,
yams, arrowroot, pine-apples, guavas, citrons and many other tropical
fruits are also cultivated, while the extensive primeval forests
abound in mahogany, cedars, rosewood, ironwood, rubber, gum copal,
vanilla, sarsaparilla, logwood and many other dye-woods, medicinal
plants, and valuable timbers. Conspicuous amongst the forest trees are
the giant ceiba, or pyramidal bombax, and the splendid Coyal palm
(_Cocos butyracea,_ L.), with feathery leaves 15 to 20 ft. long,
golden flowers 3 ft. high, and a sap which when fermented produces the
intoxicating _chicha_ or _vino de Coyol._ In Guatemala occurs the
remarkable _Herrania purpurea,_ a "Chocolate tree," whose seeds yield
a finer flavoured chocolate than the cocoa itself. The same country is
famous for its magnificent orchids, huge arborescent thistles, and a
remarkable plant called by the Spaniards _Flor de la Calentura_,
"fever flower," from the heat which it is said to emit at the moment
of fertilization. Salvador produces an abundance of medicinal plants,
notably the so-called Peruvian balsam (_Myrospermum salvatorense_); in
Honduras there are immense forests of conifers, resembling those of
the Landes in France; in Nicaragua a characteristic tree is the cortes
(_Tecoma sideroxylori_) yielding timber as hard as ebony, and
noteworthy for the golden blossom with which it is entirely covered
after the leaves have fallen.

_Inhabitants_--In 1905 the population of Central America numbered about 4,750,000, and this total tends to increase, despite the unhealthy climate of many districts, the terribly high average of infant mortality, and the slow progress of immigration. Some authorities estimate it at 5,500,000. The vast majority of the inhabitants are of mixed Indian and Spanish blood, but the Indian element predominates everywhere except in Costa Rica, where the whites are exceptionally numerous. The Indian races have not shown the same power to adapt themselves to modern civilization as the Mexicans; in some regions there are tribes remaining in a state of complete savagery although before the Spanish conquest their ancestors attained a high level of culture (see below under _Archaeology_). The density of population throughout Central America is little more than 25 per sq. m.; and it is clear that several large areas now thinly peopled once maintained a far greater number of inhabitants. Such are parts of the Nicaraguan lake district, where the flora consists in great measure of plants that were formerly cultivated by the Indians. The depopulation of these areas was effected partly by tribal wars, partly by the harsh rule of the Spaniards. Apart from the German agricultural settlements in Guatemala and elsewhere, the foreign population is chiefly confined to the seaports and other centres of commerce, Great Britain, Germany and the United States being largely represented among the wealthier classes of residents; while the foreign labourers are mostly Italians or negroes, with a few Chinese on the Pacific coast.

_History_.--Central America was discovered by Columbus in August 1502; and part of the territory which is now Costa Rica was conquered by the Spaniards under Pedro Arias de Avila after 1513. Between 1522 and 1525, the authority of Avila was superseded, and his work of conquest completed by Hernando Cortes, who had already subjugated Mexico. Panama formed part of a distinct Spanish government, "New Granada"; British Honduras was colonized, though not formally annexed, in the 18th century; and over the Mosquito Coast the British government exercised a nominal protectorate after 1665. Otherwise the rest of Central America remained a Spanish dependency bearing the general name of "Guatemala," until 1821. It ranked as a captaincy-general under the rule of a military governor, and was organized in five departments, corresponding in area with the modern republics of Guatemala, Honduras, Salvador, Nicaragua and Costa Rica. For three centuries it was administered by Spanish officials, who almost invariably devoted their whole energy to enriching themselves and the home authorities. The old Indian civilization was swept away; the native races were enslaved, maltreated and, for a time, demoralized. But their history offers no parallel to that of the West Indian Caribs, who failed to survive, and were replaced by hordes of African slaves. In Central America the Indians not only survived, thus leaving no room for any large negro population, but quickly acquired the language, religion and habits of their masters, with whom they intermarried. By the close of the 18th century, the majority had attained something like uniformity of life and thought. Racial distinctions had been obscured by intermarriage; even the term _Ladino_, or "Latin," came to mean an educated man, whether of Spanish or Indian blood. Nowhere, except in Mexico, has a mixed or coloured race more completely absorbed the civilization of its white rulers; but so gradual and silent was the process that it passed almost unnoticed. Its result, the successful revolt of the Spanish colonies--colonies mainly peopled by Indians or half-castes--was no more a conflict of rival races or civilizations than the rebellion of the British colonies in North America.