STATES OF INSECTS. (Larva.) 111 
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 larvee, 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 *. Under this head 
it may be proper to observe, that generally larvee are 
opaque; but some, as those of ants, and a few Lepi- 
doptera®, are diaphanous. That of Corethra crystallina 
(Tipula De Geer) is so beautifully transparent as to re- 
2 The larve 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. 
> Huber Fourmis, 73; N. Dict. d Hist. Nat. vi. 250. 
