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 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 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. [[File:EB1911 - Centipede Fig. 7 Scolopendra morsitans.png|thumb|left|—Scolopendra morsitans (after Buffon). A, a, Cephalic plate.

c, Tip of palpognath. e, Antenna. f, Toxicognath. ]]

''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 Newportiidae (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. [[File:EB1911 - Centipede Fig. 8 Craterostigmus.png|thumb|300px| After Pocock. Q.J.M.S. vol. 45, pl. 23, 1902.

A, Anterior end of Craterostigmus from above. a, Basal segments of antennae. c, Cephalic plate with eyes (o).

B, Maxillae. C, Palpognath. D, Toxicognath. ]]

''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.

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 1 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.

—Chilopods with a series of median