COMPLEX APPARATUS FOR NUTRITION. 85 



The activity of the digestive functions and the structure 

 of the organs, will also be regulated by a great variety of 

 other circumstances in the condition of the animal, inde-- 

 pendently of the mechanical or chemical nature of the food. 

 The greater the energy with which the more peculiarly 

 animal functions of sensation and muscular action are ex- 

 ercised, the greater must be the demand for nourishment, in 

 order to supply the expenditure of vital force created by 

 these exertions. Compared with the torpid and sluggish 

 reptile, the active and vivacious bird or quadruped requires 

 and consumes a much larger quantity of nutriment. The 

 tortoise, the turtle, the toad, the frog, and the chameleon, 

 will, indeed, live for months without taking any food. 

 Fishes, which, like reptiles, are cold-blooded animals, al- 

 though at all times exceedingly voracious when supplied 

 with food, yet can endure long fasts with impunity. 



The rapidity of development has also great influence 

 on the quantity of food which an animal requires. Thus, 

 the caterpillar, which grows very quickly, and must re- 

 peatedly throw off its integuments, during its continuance 

 in the larva state, consumes a vast quantity of food com- 

 pared with the size of its body; and hence we find it pro- 

 vided with a digestive apparatus of considerable size. 



