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.
[Illustration: FIG. 6. (After Latzel, _Die Myr. öst.-ung. Mon._ vol.
i. "Chilopoda," Vienna, 1880.)
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.
[Illustration: FIG. 7.--_Scolopendra morsitans_ (after Buffon).
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.
[Illustration: After Pocock. Q.J.M.S. vol. 45, pl. 23, 1902.