22S 



THE MECHANICAL FUNCTIONS. 



The head contains the brain, or principal enlargement of 

 the nervous system, and the organs of sensation and of mas- 

 tication. Its size, as compared with the rest of the body, 



varies much in different insects, and is in general propor- 

 tionably larger than it is in the larva state. Its integument, 

 which, from analogy with vertebrated animals, has been 

 called the skull, or cranmm, (c, Fig. 150,) is usually the 

 hardest part of the general crust. Although it may appear, 

 on a superficial examination, to consist of a single undivided 

 piece, yet, on tracing its gradual formation, it is found to be 

 in reality composed of a union of several of the segments of 

 the larva. Audouin and Carus distinguish three component 



