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.

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.

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.

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.

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.

After Pocock. Q.J.M.S. vol. 45, pl. 23, 1902.
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.