INSECTS. 



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 (G-rylli, 

 Locustce) 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 larvae 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 Lygceus apterus FABR.) ; in 

 Cicada orni the intestinal canal is about ten times as long as the 

 body 1 . Amongst Coleoptera the Scarabceides, 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 LON DUFOUR, Recherches anat. et physiol. sur les H&mipt&res (Extrait det Mim. 

 des savans etrangers, Tom. IV.) Paris, 1833, 4to. p. 92, PL VIII. fig. 95. 



