138 



AKTHROPODA 



similar to that occurring in the larviB of insects. The hard 

 covering becomes too small for the growing animal, and 



in the lobster it ^ 



splits along the 

 median dorsal line, 

 while the blood 

 leaves the limbs, 

 permitting them 

 to be withdrawn 

 from their case- 

 ments. The lining 

 of the whole ali- 

 mentary canal is 

 also shed. The 

 animal just before 

 molting is known 

 as the black lobster. 

 The newly molted 

 crab is marketed 

 under the name of 

 soft-shelled crab. 



The hermit crabs 

 protect themselves 

 by living in the 

 abandoned shells 

 of some mollusks, 

 and when the in- 

 creased size of the 

 body makes the shell too small, the animal seeks a 

 larger one. Of the edible crabs, the commonest are the 

 large blue crab (Callinectes hastatus), and the oyster 



FIG. 160. Photograph of Cyclops enlarged forty 

 times. An egg mass at the right. 



