282 NATURAL THEOLOGY. 



cribed as an organ of mastication, in which there 

 is an incessant and alternate action of opponent 

 muscles, as in the motions of the jaws. In the 

 stomach of the lobster we have not merely the 

 muscles of mastication, but the teeth also : so that 

 it appears the function may be performed alto- 

 gether internally, and without the volition, and 

 probably without the sensations, that accompany 

 the offices of the mouth. We mention this, as 

 drawing the reader to comprehend that many 

 organs may be in operation in the internal econo- 

 my, without our consciousness. 



Our author, w^ith much propriety, from time to 



time, adverts to those changes in the organization 



which accommodate the animal to new conditions, 



Now, in terrestrial animals, the act of swallowing 



must be accommodated to the atmosphere ; but 



if the animal lives in water, and still breathes the 



air, the structure of the parts must be changed. 



The crocodile seizes its prey, and descends into 



the water with it. Its power of descending does 



not, as in the fish, result from compressing the 



air-bladder: but is owing, as we have shown, to 



a provision in its ribs and lungs. Unless the 



crocodile could expel the air from its lungs in a 



greater degree than the mammalia are capable of 



doing, it could not crawl upon the bottom, nor 



retain its place there without continual exertion. 



