LOBSTERS. 



-d 



have five, but the wood- 

 louse has seven pairs of 

 legs. The head is pro- 

 vided in front with two 

 pairs of appendages, 

 called antennse (->f,fig. 

 61), and is also furnish- 

 ed with several pairs of 

 jaws, and the abdomen 

 bears other appendages 

 in form of fins. An 

 examination of the 

 figure (61), which re- 

 presents a lobster, will 

 enable us better to un- 

 derstand the various 

 parts of crusta'ceans: 

 a, the carapace, or com- 

 mon integument of the 

 head and thorax ; 6, 

 the abdomen, composed 

 of seven rings ; c, the 

 caudal fin ; d, the 

 eyes; e, the internal 

 antennse ; f, the ex- 

 ternal antennas ; g, the 

 palpi, which are articu- 

 lated filaments attached 

 to the jaws or to the 

 lower lip, and appear 

 to be employed by the 

 animal in recognising 

 its food; 7i, the first 

 pair of legs, called 



chelcB (from the Greek, chele, pincers) ; ^, the second pair of 

 legs, also terminated by pincers; j, the third pair of legs, ter- 

 minated by pincers, and termed foot-jaws ; k, the fourth pair; 

 I, the fifth pair of legs. 



4. The external skeleton of crusta'ceans is formed of an ex- 

 tremely hard epidermis : at certain periods it is detached and falls 

 off. The necessity for such changes or moulting in animals, 

 whose body is enclosed in a hard sheath, is very plain ; for inas- 

 much as this sheath does not grow or enlarge, like the internal 

 parts, it would oppose an insurmountable obstacle to their develop- 



ft 



r. 61. LOBSTER. 



4. What kind of skeleton do Crusta'ceans 

 preserve the same covering ? 



possess? Do they always 



