INSECTS. yt 5, 
~ 
in some insects harder, horny and opaque; they are then called wing- 
covers (elytra), and the under-wings, usually larger, are when at 
rest folded transversely beneath the covers and concealed (as in 
Beetles, Coleoptera). In other instances the under wings disappear, 
and the wing-covers coalesce by their inner edges (elytra coadu- 
nata). Hemelytra is the name given to the anterior wings, when 
horny or coriaceous at the base but membraneous towards the apex 
(in Hemiptera, as Water-scorpions, Nepa cinerea, &c.) 
The hinder-body (abdomen) constitutes, the third portion of the 
body of Insects, and usually consists of nine rings, of which 
however the last are in some instances so much concealed, and in 
others so small or so fused with the preceding, that they seem to 
be entirely wanting. As the organs of sense have their seat in 
the head, and those of motion in the thorax, so do the principal 
organs of vegetative or organic life reside in the abdomen. 
The digestive organs present differences according to the 
Orders and Families. Here the comparative length of the intes- 
tinal canal does not always depend, as in vertebrate animals, upon 
the nature of the food, and many species that live on animal 
substances have a longer and more convoluted canal than others 
which live on plants; in Grasshoppers for instance (Gryll, 
Locuste) it is almost straight, though these insects live exclusively 
on vegetable food. In those Insects whose body consists of 
uniform rings (as the myriapods) and in vermiform larvee of Insects 
with a complete Metamorphosis, the intestinal canal is straight, or 
makes only few and inconspicuous curves. ‘The intestine has the 
greatest length in proportion to the body in certain Coleoptera and 
Hemiptera. In the last it is at least twice, often four or five times 
the length of the body (ex. gr. in Lygeus apterus FAasrR.); in 
Cicada ornt the intestinal canal is about ten times as long as the 
body!. Amongst Coleoptera the Scarabeides, to which the common 
cockchafer belongs, are remarkable for their very long and tortuous 
intestinal canal, which in Copris lunaris measures ten or twelve 
times the length of the body. 
The membranes or coats of the intestinal canal are, first, a thin 
covering, which without sufficient reason has been compared with 
1 Léon Durour, Recherches anat. et physiol. sur les Hémiptéres (Extrait des Mém. 
des savans étrangers, Tom. Iv.) Paris, 1833, 4to. p. 92, Pl. vu. fig. 95. 
