211 



CHAPTEE XI. 



CRUSTACEA. 



NATURE AND CONSTRUCTION. — EXUVIATION. — CASTING LIMBS.— METAMOR- 

 PHOSES. — THE PRAWN, PAL^^MON SERRATUS. — THE COMMON SHRIMP. — 

 THE COMMON LOBSTER. 



Crabs, Lobsters, and Shrimps, are the most familiar forms 

 of this curious class of marine animals. They are all jointed 

 animals, the body being composed of distinct segments; they 

 have jointed limbs, also composed of distinct, movable seg- 

 ments ; they breathe by means of gills, which are in some 

 cases covered and in others exposed. With very few excep- 

 tions they have two compound eyes ; generally four antennse, 

 three pairs of masticating jaws, and two or three pairs of 

 foot-jaws, in descriptions called '' joedijoalps /' the second 

 and third pairs of foot-jaws sometimes assuming such shape 

 and functions that they may be interchangeably called foot- 

 jaws, or a sixth and seventh pair of legs. Accordingly, they 



