132 



COMPARATIVE ZOOLOGY. 



mature form. This moulting is a very remarkable opera- 

 tion. How the Lobster can draw its legs from their cases 



without unjointing 

 or splitting them 

 was long a puz- 

 zle. The flesh be- 

 comes soft, and is 

 drawn through the 

 joints, the wounds 

 thus caused quickly 

 healing. The cast- 

 off skeleton is a per- 

 fect copy of the an- 

 imal, retaining in 

 their places the del- 

 icate coverings of 

 the eyes and anten- 

 nae, and even the 



FIG. 98. Diagram of nn Insect: A, head bearing the Ijnincr membrane of 

 eyes aud antennae; B, prothorax, carrying the first 



pair of legs; C, mesothorax, carrying the second the Stomach With its 

 pair of legs and first pair of wings ; D, carrying the , 



third pair of legs and second pair of wings; E, ab- teeth, 

 domen, with ovipositor, F; 1, coxa, or hip; 2, tro- nni -i , 



chanter ; 3, femur, or thigh ; 4, tibia, or shank ; 5, tar- U J 



BUB, or foot ; 6, claw. o f I nsects differs 



from that of Crustaceans in consisting mainly of a horny 

 substance called chitine and in containing no lime. The 

 head, thorax, and abdomen are distinct, and usually con- 

 sist of fourteen visible segments one for the head, three 

 for the thorax (called prothorax, mesothorax, and metaiho- 

 rax\ and ten for the abdomen. The antennae, or feelers, 

 legs, and wings, as well as hairs, spines, and scales, are ap- 

 pendages of the skeleton. As Insects grow only during 

 the larval, or caterpillar, state, moulting is confined to that 

 period. These skeletons are epidermal, deposited in suc- 

 cessive layers, from the inside, and are, therefore, capable 

 of but slight enlargement when once formed. 



