532 PHILOSOPHY OF ZOOLOGY. 



Traces of the organs of hearing may be detected in some 

 of the larger Crustacea. In the cray-fish, there is a purse- 

 shaped labyrinth at the base of each antenna, covered ex- 

 ternally by an elastic membrane or tympanum, and open at 

 its central extremity for the passage of the auditory nerves. 

 No traces of the organs of hearing have been detected in 

 insects. Yet insects emit a variety of sounds by the fric- 

 tion produced by their mandibles, their wings, and their 

 legs, which are communicated to others, and understood by 

 them. The proofs of the existence of taste and smell in 

 the different tribes, rest on the same foundation, the evi- 

 dence of the function being performed. These senses are 

 chiefly used in the animal economy in subserviency to the 

 digestive system. The organs in which they reside are pro- 

 bably the palpi, or the other more flexible parts of the 

 mouth. But these parts are so different in their form from 

 the organs employed for the same purpose in the higher 

 classes of animals, and so diminutive in size, that neither 

 analogy nor dissection can be called in to illustrate the sub- 

 ject. 



In treating of the important object of nutrition, it is ne- 

 cessary to begin with a description of the parts employed 

 in procuring and preparing food for the gullet. In many 

 cases, as in the higher orders of animals, the legs, particu- 

 larly the first pair, execute the first movement of seizing 

 the food and conveying it to the mouth ; in general, how- 

 ever, the parts of the mouth, unassisted, seize, cut, bruise, 

 and prepare the food for the gullet. 



The masticating organs, in their simplest form, in- 

 clude the four following parts (which we shall designate 

 by their Latin appellations, for want of appropriate Eng- 

 lish terms), Labrum, Mandibulae, Maxillae, and Labium. 

 These form the mouth, and are denominated Instrumenta 

 ciharia. 



