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 so that the antennae can be protruded or withdrawn 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 larvae is in most cases rapid. The 

 whole structure of the animal, indeed, indicates pro- 

 vision for its speedy increase in size. The Icst 



* See Naturalist's Library Entomology, British 

 terflies. 



