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 



membrane of 



Pio. 98. Diagram of an Insect: A, head bearing the 

 eyes and 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, metathorax, 

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

 wings; E, abdomen, with ovipositor, F; 1, coxa, or mi l irkrnv r>rncf 

 hip; 2, trochanter; 3, femur, or thigh; 4, tibia, or rn j 



shank ; 5, tarsus, or foot ; 6, claw. Q f I nse cts 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 prothorax, mesoihorax, and metatho- 

 raa?), 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. 



