152 LIFE BY THE SEASHORE. 



bilaterally symmetrical. All are invested with a firm 

 cuticle of chitin, are furnished with jointed hollow limbs, 

 and in each case the body consists of a series of similar 

 parts or segments, least obvious in the crab. Because of 

 these characters all are Arthropods. Further, we include 

 them in the class Crustacea because all have two pairs of 

 feelers (antennae), a shell containing carbonate of lime, and 

 all breathe by gills. The last-named structures may be 

 readily seen in prawn and lobster by gently raising the 



FIG. 48. Common lobster (Homarus vulgaris). 



large flaps at the sides of the body in the anterior region. 

 Beneath these lie delicate structures, shaped like bottle- 

 brushes, and closely connected with the limbs. In the crab 

 the gills are so well protected by the shell as not to be seen 

 without dissection. 



Looking now at our specimens in somewhat greater detail 

 we see that the prawn and lobster or crayfish resemble one 

 another in that in both the body consists of an anterior, not 



