CRUSTACEA. 



227 



number thus taken upon the shores of New England and 

 Canada amounts to between twenty and thirty million 

 annually. Overfishing is, 

 however, rapidly reducing 

 the numbers caught. Cray- 

 fish are used largely as 

 food in Europe, and are 

 bred in ponds for the mar- 

 ket, but in America they 



i/ 



are largely neglected. 

 Shrimps and prawns are 

 mostly salt- water forms, but 

 some of the prawns occur in 

 fresh water in the warmer 

 parts of the world. The 

 line between the two is not 

 ' easily drawn except by say- 

 ing that the body of the 

 shrimp (fig. 54) is flat- 

 tened (depressed) from 

 above downwards, while 

 that of the prawn is com- 

 pressed (flattened from side 

 to side). In America, 



FIG. 54. Common shrimp (Lrangon 

 ' Shrimp Salad ' is almost vulgaris). From Emerton. 



universally made from prawns. 



Of the Anomura, the most interesting are the so-called 

 hermit-crabs (fig. 55). These are somewhat lobster-like, 

 but the abdomen is but slightly hardened, and so, to 

 protect this vulnerable part of the body, the crab inserts 

 it in a deserted snail-shell, and this 'house' he carries 

 about with him wherever he goes, retreating into it and 

 closing the opening at the approach of danger with his 



