182 



PHYSIOLOGY 



(centipeds), (Fig. 100), or two (millipeds), (Fig. 101), 

 pairs of appendages. 



Insecta. — (Hexapoda). — The study of insects is a 

 science in itself. There are supposed to be more than 

 a million distinct forms and more species than in 

 all the rest of the animal king- 

 dom. The body is divided into 

 three distinct regions. The head 

 bears the antennae, the sense or- 

 gans and the mouth parts. These 

 are fitted for biting or for suck- 

 ing. The thorax is made of 

 three segments which may be 

 movable. On it are three pairs 

 of legs, and usually two pairs of 

 wings, but these may be entirely 

 missing or one pair may be re- 

 duced or hardened. The ab- 

 domen is made of ten segments, 

 though the number may be re- 

 duced. It may be fixed to the 

 thorax by its entire width or by 

 a slender stalk. It may have 

 three pairs of appendages, but 

 these are never locomotor in the 

 adult. They may be rudimen- 

 tary or they may be transformed into the organ which is 

 used for laying the eggs or for stinging. The sexes are 

 separate. 



The alimentary canal has few convolutions (Fig. 

 102). There is a chewing stomach and a true stomach. 



Fig. 100.— Centiped. 



