.* I ORGANS OF SUPPORT, 



of an upper and a lower arched plate, attached by a softer 

 flexible portion of the skin upon the two sides, and generally 

 each segment presents but one pair of extremities more 

 lengthened than in the iuli. The first pair of feet are here 

 in form of simple curved perforated hooks placed at the 

 sides of the mouth, and the succeeding feet along the whole 

 sides of the trunk terminate in a single sharp conical claw 

 less curved, with a very minute oppo sable spine extending 

 from the interior of each terminal joint. The antennae (Fig. 

 1 5, c, c) are two in number, as in insects, and for the most 

 part long, filiform, and multi-articulate, and the organs of 

 vision generally consist of numerous simple eyes placed in a 

 group behind the bases of the antennae. 



In the cylindrical vermiform chilognatha, the mandibles 

 appear to be still destitute of palpi, which are developed on the 

 mandibles of the larger chilopoda. The segments of the head, 

 thorax, and abdomen are scarcely yet distinguishable from each 

 other. The stigmata for respiration open on the sides of the 

 alternate rings of the trunk, as if these were equivalent to only a 

 half of the ordinary rings or segments of insects. The two last 

 pairs of feet (Fig J 5.e, e) generally extend backwards in form of 

 a bifid tail: they are for the most part longer than the other feet, 

 and sometimes form foliated expansions at their free extremi- 

 ties, as we likewise often see in the Crustacea. The segments 

 of the trunk lie over each other in an imbricated manner at 

 their line of junction, so as to defend the internal soft parts 

 during the bending serpentine motions of the body. These 

 animals do not undergo metamorphoses like insects, nor ac- 

 quire wings, but the number of their segments varies with 

 their period of growth ; and from the density of their exter- 

 nal coverings, their unorganized nature, and their enveloping 

 tubular forms, they are exuviable, like the dense skeletons 

 of all the articulated tribes with articulated members. 



XI. Insect a. The skeleton of insects, from its super- 

 ficial position, and from the lightness and density of its 

 materials, is well adapted for intevertebrated animals 

 destined for an aerial life. It is composed, in its densest 

 parts, of a thin epidermic layer, a colouring matter often 

 presenting the most lively hues, and a brilliant metallic 

 lustre, and a thicker internal layer much resembling the 

 woody fibres of plants, but composed of peculiar animal 



