82 
INTRODUCTION TO 
detected. Not rarely, however, they are pretty con- 
spicuous, consisting of four or five joints in the ma- 
jority of beetles, and of two or three in caterpillars. 
The joints are frequently contractile within each other, 
so that the antenna* can be protruded or withdrawn 
at the pleasure of the animal. 
The head of larvae is usually of a harder substance 
than the rest of the body, and in that case is com- 
monly of a triangular or orbicular shape ; but its 
covering among the diptera is soft and membranous, 
from which results the singular anomaly that it is 
capable of dilatation and contraction, and therefore 
of assuming any form the insect may desire. The 
remarkable spines that arm the heads of many foreign 
caterpillars have been already mentioned.* 
On the various and numerous appendages of larvae, 
whether serving for respiration, ornament, or defence, 
it is unnecessary to enlarge in this place, as it would 
only be anticipating what can be more appropriately 
introduced hereafter. Their anatomy will be con- 
sidered conjointly with that of the perfect insects. But 
there are other interesting features in their history, 
to which it will be most convenient to advert in this 
place, namely, their growth, moulting, and prepara- 
tions for entering upon the pupal or penultimate 
state. 
The growth of larva* is in most cases rapid. The 
whole structure of the animal, indeed, indicates pro- 
vision for its speedy increase in size. The instru- 
* See Naturalist’s Library— Entomology, British But- 
terflies. 
