or adult animal, but subject to important and very remarkable varieties during the progress of its growth. In the lower forms, such as Julus (fig. 304), the texture of the segments is hard, crustaceous, and brittle; but in the Scolopendroid races, the rings are flattened and covered above and below with tough and coriaceous scuts. In all the Chilopoda each segment supports only a single pair of ambu latory legs, which resemble in many respects those of insects, but terminate invariably in a simple claw. In the Chilognatha, on the contrary, with the exception of a few of the most anterior, and likewise of the terminal or anal segments, each ring has two pairs of feet attached to its under surface, con sisting apparently of two half segments con joined ; and this view of their composition is further strengthened by the fact, that a deep transverse indentation or groove is always visi ble upon the dorsal surface, dividing the other wise apparently single ring into an anterior and a posterior moiety, to each of which is fixed a pair of short and very feeble legs, com posed of several distinct articulations. The three first segments in Julus form exceptions, however, to this arrangement, each of these supporting only a single pair of ambulatory feet, and these segments have been supposed by some authors to represent the thoracic seg ments of the true insects. The seventh ring, likewise, in the female, has one pair deficient, they being replaced by the orifices leading to the sexual organs. The anal and penultimate segments are completely apodal in the Julidx, whilst, on the contrary, in some of the Chi lognatha, the size of the locomotive limbs in creases progressively as we approach the caudal extremity, the last segment supporting the longest pair, which are directed backwards, so as to have in some measure the appearance of a furcate tail.
In the Scolopendridx ( Chilopod a, Latr.), a family which embraces those forms of Myria poda that are most nearly allied to Insects, we have a race of carnivorous Myriapods, pos sessed of strong and active limbs, varying in number in different genera from fifteen to twenty-one pairs, by the aid of which they can run with considerable rapidity, and are able, owing to the flexibility of their long and jointed bodies, to wind their way with facility among the lurking places of Insects, against which they carry on an unrelenting warfare. All of them are found carefully to avoid the light, and generally to frequent damp situations, more especially where decaying animal or vege table substances abound. They lurk, therefore, under stones or pieces of old wood, or are met with beneath the bark of trees, localities which from their structure they are peculiarly adapted to occupy.
In the following account of the anatomy of these creatures we shall select the Scolo pendrir, properly so called, for particular de scription, as being the largest and, conse quently, most commonly met with in our collections, noticing, however, as we proceed, such peculiarities as may be worthy of notice in other genera.
The Scolopendra have their bodies corn. posed of twenty-one segments exclusive of the head, to each of which is attached a pair of jointed legs. The segments are all of them more or less quadrilateral in their shape, their transverse diameter being generally the longest, but their size is very variable and irregular.
The whole body is depressed, each segment, consisting of a dorsal and a ventral plate of soft but comeous consistency, formed by a thickening of the cuticle in those regions of the body, while the sides to which the legs are appended, and where, moreover, the respiratory spiracles are situated, are soft and of a coria ceous texture.
The legs are all five-jointed and terminated in a simple sharp horny claw; those appended to the segments in the neighbourhood of the head are comparatively small, but as they ap proximate the hinder part of the body they increase in size and strength, the last pair being turned backwards so as scarcely to be useful as locomotive agents.
The head, and more especially the parts entering into the construction of the oral ap paratus of these Myriapoda, present many difficult inquiries to the scientific entomologist, who would attempt to identify them with ap parently corresponding structures met with in the organization of the mouth of insects, and accordingly we are not at all surprised to find that no two authors agree as to the names that are most applicable to the different pieces be longing to this portion of their economy. The Myriapoda, be it remembered, are obviously an osculant or transition group allied at once to the Annelidans, to the Insecta, to the Arach nidans, and to the Crustacea. It is by no means surprising, therefore, that, in the con struction of almost every part of their bodies, we find an organization intermediate between these important divisions of articulated animals, as we shall again and again have occasion to no tice. But, perhaps, in no part of their economy is this intermediate structure better exemplified than in the mouth of the Scolopendra, to the different portions of which all writers appear to have given names rather in conformity with their own preconceptions than with any real affinities that have been pointed out, or any general view of the real nature of such appen dages. With all respect for the opinions of preceding writers, we shall, on this account, endeavour, in the following description, to avoid as much as possible technicalities pecu liar to the orismology of any particular branch of zoological science.
The head of a Scolopendra, or that portion of the creature which supports the instruments or sensation and the organs employed for the prehension of food, appears, when viewed superficially, to consist of two segments, one a circular shield-like plate, constituting the real head, that exists only upon the dorsal aspect of the body, in which are inserted the antennae, and which, moreover, contains the eyes and overlaps the greater number of the pieces belonging to the mouth. The second segment, by far the larger and the stronger of the two, and, in fact, from the density of its corneous envelope, the strongest segment of the whole body, is entirely devoted to the support and movement of a pair of sharp bi-articulate and hooked fangs resembling jaws, that move trans versely like the (so-called) mandibles of a Spider, but which are in reality only modifica tions of the ambulatory feet converted into instruments for killing prey, each being per forated near its sharp termination with a long oval slit, through which venom is said to be instilled into the wound inflicted by this formidable weapon.