PHYSIOLOGY OF INSECTS. 155 



perception, appear infinite ; they pervade the 

 skin, muscles, nerves, stomach, intestines, legs, 

 wings, and all the organs of sensation ; the 

 organs of respiration are therefore more generally 

 diffused in insects than in other animals. 



588. The blood of animals, in order to main- 

 tain its vital powers, requires supplies of oxygen, 

 which is a principal ingredient of atmospheric 

 air: an animal, therefore, in breathing the air, 

 divides the oxygen from the other constituent 

 parts, appropriates the former, and rejects the 

 latter. 



