STATES OF INSECTfj. Ill 



interior of the body of these animals is generally of a 

 softer consistence than in the perfect insect. Their in- 

 testines, and other internal organs, are usually wrapped 

 in a voluminous substance of a fatty nature, which is re- 

 garded as analogous to the epiploon, omentum, or caul, 

 which envelops the viscera of quadrupeds, &c, and is 

 called by Reaumur the corps graisseux. The use of this 

 general flexibility of larvae is obvious ; for, their bodies 

 being mostly long and narrow, a hard rigid covering 

 would have been very inconvenient, and a considerable 

 impediment to their motions. When a caterpillar is 

 feeding, it has occasion to apply its body to any part of 

 the margin of a leaf so as to support itself by its prolegs, 

 and when moving it wants to give it all the curves that 

 are necessary to enable it to avoid obstacles, and thread 

 its way through the sinuous labyrinths which it must 

 often traverse. On the other hand, the hardness of the 

 substance of its head affords a strong fulcrum to the 

 muscles which keep its powerful jaws in constant play. 

 The larvae, indeed, of some Diptera have a membra- 

 nous head; but their mandibles, which serve also as 

 legs, are not grinders, but merely claws, the muscles of 

 which require less powerful support 3 . Under this head 

 it may be proper to observe, that generally larvae are 

 opaque ; but some, as those of ants, and a few Lepido- 

 ptera b , are diaphanous. That of Corethra crystallina 

 (Tipula De Geer) is so beautifully transparent as to re- 



a The larvae described in the first Section, which resemble the 

 imago, are usually covered with a skin not materially different from 

 that of the insect in that state. 



b Huber Fourmis. 73; 2V". Diet. d'Jiist. Nat. vi. 250. 



