Chilopoda

“ In some a serial arrangement of stigmata comparable to that observed in Chilopoda is found. In other cases (some larvae) stigmata are absent; in other cases again a single stigma is developed, as in the smaller Arachnida and Chilopoda, in the median dorsal line or other unexpected position. When the facile tendency of Arthropoda to develop tracheal air-tubes is admitted, it becomes probable that the tracheae of Hexapods do not all belong to one original system, but may be accounted for by new developments within the group. ”

“ I have therefore divided the Diplopoda into two suborders, the Chilognatha and Sugentia, retaining old names, but giving new significance to them. The minor characters have seemed to me to confirm this, and to indicate that it is coincident with the plan on which the Myriapoda have been created. M. Brandt (Recueil, p. 26) divides the Chilopoda into the Schizotarsia and Holotarsia. ”

“ Moreover, the recent researches of Heymons into the embryology of Scolopendra, one of the Chilopods, has shown a close correspondence in the number of cephalic metameres between the Chilopoda and Hexapoda, a correspondence which has not yet been established in the case of the Diplopoda or Symphyla. This last discovery bears out the view of relationship between the centipedes and insects, to the exclusion of the Diplopoda, Symphyla and Pauropoda. ”

“ The shape of the body is short, thick, and very compact. The composition of the individual segments resembles that found in Chilopoda rather than that of Chilognatha.
The antennae are very long, longer than in any of the Chilopods, and are composed of a great number of very small joints. The mouth parts show a greater length and slenderness than do those of the other Orders mentioned as yet. They consist of—
1. ”

“ 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 ”

“ 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. ”

“ On glancing over the Chilopoda it will be seen that, as we descend the scale, the number of segments in the body constantly increases—or, in other words, the distinctive character which separates the Myriapods from the Hexapods and Crustacea, and allies them to the Annelids,—the multiplicity of segments, the absence of cephalization—is exaggerated. On applying this principle, it will be at once perceived that the Polydesmidæ must be placed above the Iulidæ, and the Glomeridæ, Leach (of Newport) , be still higher, and thus be thrown next to the first order. ”

“ Myriapods are hatched at different stages of development. The Chilognatha have only three appendages, which are so little developed that they are only small shapeless stumps, while {67}the Chilopoda have the full number of legs in some cases; in others only a small number of legs, but yet more than the three pairs of legs of the Chilognatha, and fully developed instead of stump-like. The eyes are usually developed late in the life of the young animal. The bursting of the egg-shell is assisted in some Myriapods by a special kind of spike on the back part of the head. ”

“ CLASS SYMPHYLA.
Prosogoneate Arthropods, differing in many important particulars from the Diplopoda and Pauropoda. The axis of the head lies in the same straight line as that of the body, as in the Chilopoda, and not at right angles to it as in the Diplopoda and Pauropoda. There are no eyes. The antennae are very long and many-jointed. Four pairs of gnathites attached to the under-side of the head have been detected. The first pair (mandibles) are two-jointed, as in many Diplopods. ”

“ Newport and others have not allowed these characters the weight that they deserve. Mr. Gray does not even allow them generic force, if his classification (Cyclop. Anat. and Physiol., art. Myriap.) is to be trusted. Or was he entirely ignorant of their existence! Newport gives to them a family significance.
The different structure of the mouth, and the consequent different food and habits of living, although not sufficient to stand in competition with the characters separating the Chilopoda and Diplopoda, are still of higher import than any other differences in the latter order. ”

“ Diagnostic or essential characters of Symphyla.—Head shaped as in Thysanura (Cinura) , with the Y-shaped tergal suture, which occurs commonly in insects (Thysanura, Collembola, Dermaptera, Orthoptera, Platyptera, Neuroptera, etc.) , but is wanting in Myriopoda (Diplopoda and Chilopoda) ; antennæ [8] unlike those of Myriopoda in being very long, slender, and moniliform. Clypeus distinct. Labrum emarginate, with six converging teeth. Mandibles 2–jointed, consisting of a vestigial stipes and distal or molar joint, the latter with eight teeth. ”

“ Fossil remains of the Chilopoda are first met with in the Jura period.
The third and last class of the Arthropoda breathing through tracheæ, is that of the Flies, or Insects, in the narrow sense of the word (Insecta, or Hexapoda) , the largest of all185 classes of animals, and next to that of Mammalia, also the most important. Although Flies develop a greater variety of genera and species than all other animals taken together, yet these are all in reality only superficial variations of a single type, which is entirely and constantly preserved in its essential characteristics. ”

“ The endopodite may be retained as a small segmented palp at the side of the gnathobase or disappear (mandible of Crustacea, Chilopoda and Hexapoda) .
(9) The corm becomes the seat of a development of a special visual organ, the Arthropod eye (as opposed to the Chaetopod eye) . Its jointing (segmentation) may be retained, but its rami disappear (Podophthalmous Crustacea) . Usually it becomes atrophied, leaving the eye as a sessile organ upon the prae-oral region of the body (the eye-stalk and sessile lateral eyes of Arthropoda generally, exclusive of Peripatus) . ”

“ It is most probable that the young is hexapodous, since the first pair of limbs are 4–jointed, all the rest 5–jointed; while Newport, and also Ryder, observed specimens with nine, ten, eleven, and twelve pairs, and Wood-Mason confirms their observations, “which prove that a pair of legs 25is added at each moult,” and he concludes that the addition of new segments “therefore takes place in this animal by the intercalation of two at each moult between the antepenultimate and penultimate sterna, as in the Chilognatha, and as also in some of the Chilopoda.” ”

“ The Diplopods depend upon the vegetable kingdom for their sustenance. The body is much more rigid than in the Chilopods, from the close conjunction, or often imbrication, of the segments, and the inflexibility of the segments themselves, caused by the density and thickness of the scuta aud sterna and the absence of lateral membranes. For this reason the Diplopoda possess but little or none of that power of raising and twisting the body, which is so annoying to the collector of tropical Scolopendra. ”

“ The arrangement of the tracheæ and stigmata is much as in insects, but in the Diplopoda the tracheary system is more primitive than in chilopods, a pair of stigmata and a pair of tracheal bundles occurring in each segment, while the bundles are not connected by anastomosing branches, branched tracheæ only occurring in the Glomeridæ. The tracheæ themselves are without spiral threads (tænidia) . It is noteworthy that the tracheæ arise much later than in insects, not appearing until the animal is hatched; in this respect the myriopods approximate Peripatus. ”

“ The important array of characters which separates the Euphausiidae from the other Schizopods and unites them with the Decapoda can no longer be neglected, and the consideration of Anaspides and its allies will further emphasise the extreme difficulty of retaining the Schizopoda as a natural group. In the sequel Calman’s proposed scheme will be adopted.
DIVISION 1. SYNCARIDA. There is no carapace, and all the eight thoracic segments may be free and distinct. Eyes may be pedunculate or sessile. The mandible is without a lacinia mobilis. ”

“ The body of the embryo shortly before hatching is cylindrical; the sternal region is much narrower than in the adult, hence the insertions of the feet are nearer together, while the first six pairs of appendages begin to grow out before the hinder ones. Thus the first six pairs of appendages of the embryo Geophilus correspond to the antennæ, two pairs of jaws, and three pairs of legs of the larval Julus. These features appear to indicate that the chilopods may be an offshoot from the diplopod stem. ”

“ The genital glands lie beneath, while in chilopods they lie above the intestine; this, as Korschelt and Heider state, being a more primitive relation, since in Peripatus they also lie above the digestive canal.
The nervous system of diplopods is not only remarkable for the lack of the tendency towards a fusion of the ganglia observable in insects, but for the fact that the double segments are each provided with two ganglia. The brain also is very small in proportion to the ventral cord, the nervous system being in its general appearance somewhat as in caterpillars. ”

“ Certainly Scolopendrella is the only extant arthropod which, with the sole exception of the anteriorly situated genital opening, fulfils the conditions required of an ancestor of Thysanura, and through them of the winged insects. No one has been so bold as to suggest the derivation of insects from either diplopods or chilopods, while their origin from a form similar to Scolopendrella seems not improbable. Yet Uzel has very recently discovered that Campodea develops in some respects like Geophilus, the primitive band sinking in its middle into the yolk, with other features as in chilopods. ”

“ In some way not yet understood, the embryos penetrate into the body cavity of the Cyclops, where they undergo a metamorphosis. For their further development it is necessary that the Cyclops should be swallowed by man, as may easily happen in drinking water from a pond. When the Cyclops is digested the larval worms are set free, and they bore their way through the tissues of their human host till they reach the place (generally under the skin of the leg) where they complete their development and produce the innumerable embryos that are set free in the way just described. ”

“ 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. ”

“ In some Phyllopoda (Apus) egg-sacs are formed by modification of certain of the thoracic feet. The eggs are retained between the valves of the shell in some Phyllopoda and in the Cladocera and Ostracoda, and they lie in the mantle cavity in the Cirripedia. In the Copepoda they are agglutinated together into masses attached to the body of the female. Among the Malacostraca some Schizopoda, the Cumacea, Tanaidacea, Isopoda and Amphipoda (sometimes grouped all together as Peracarida) have a marsupium or brood-pouch formed by overlapping plates attached to the bases of some of the thoracic legs. ”

“ The following five "families" are composed of degraded forms of various descent. Most of them lead a burrowing, subterranean life, in adaptation to which the body has become snake-shaped or worm-like. The fore-limbs are entirely absent, except in Chirotes; the hind-limbs are absent, or reduced to small flaps; the girdles are reduced correspondingly. The skull is devoid of postorbital, postfronto-squamosal, supratemporal, and jugal arches. The quadrate bone is mostly immovable. The eyes and ears are concealed, except in the Pygopodidae. ”

“ When these animals are hunted much, they become proportionably wary, but here no hunter ever troubles them, and they repose in security, always however taking the precaution of sleeping just above the deep channel, into which they can plunge when alarmed. When a shot is fired into a sleeping herd, all start up on their feet, and stare with peculiar stolid looks of hippopotamic surprise, and wait for another shot before dashing into deep water. A few miles below Chikumbula's we saw a white hippopotamus in a herd. ”

“ So again, if we were to attempt to class the six species of Scalpellum by their males and complemental males, undoubtedly the first three and last three species of the genus would have to stand in distinct orders! Hence we may reject the males as a foundation for classification, but no doubt they serve to show that the resemblances in the carapaces of Alcippe and Cryptophialus, are not merely analogical or functional, but evince a true affinity, though these genera differ so greatly, in mouth, body, œsophagus, cirri, and especially in their metamorphoses. ”