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 quicklj 

 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 oti Insect: A, tead bearing the lininfiT membrane of 

 eyes and antennae; B, ])rothorax, ciu't-ying the first ^ 



pair of legs; C, meaothorax, carrying the second the Stomach with itS 

 pair of legs and first pair of wings ; D, meiathorax, , 



carrying the third pair of legs and second pair of teCtn. 

 wings ; E, abdomen, with ovipositor, P ; 1, coxa, or mi lin^m, nr-nat- 

 hip; 2, trochanter; 3, femnr, or thigh; 4, tibia, or ■'•"*' iioi Iiy CI U&L 

 shank ; 5, tarsus, or foot ; 6, claw. q£ InsectS differs 



from that of Crustaceans in consisting mainly of a horny 

 substance called chitin 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 pj'othorax, mesothorax, and metatho- 

 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. 



