144 FIRST BOOK OF ZOOLOGY. 



the hermit-crab gets too big for it. The creature has, there- 

 fore, to go in search of another house slightly bigger than 

 the one ready to be discarded. It is said that it does not 

 always content itself with the dead shells that strew the 

 beach, but has been seen attacking a live snail and eating it 

 for the purpose of occupying its vacant shell, and this is 

 rendered probable by the fact that they so often occupy 

 fresh and perfect shells. 



Not unfrecjuently they are found living in old and beach- 

 worn shells which they have dragged about so long as to 

 have worn the shell nearly through at the place where it 

 rests and rubs against the sand. The pupils may collect 

 hermit-crabs of all sizes on the shores. 



The figure on the preceding page represents a hermit- 

 crab after its removal from the shell. The creature is 

 drawn as it appears lying on its back. 



132. There are comparatively few species of crustaceans 

 found in fresh water ; and, with the exception of the species 

 of crawfish and a few others, the fresh-water crustaceans are 

 of small size. 



FIG. 134. FRESH-WATER CRUSTACEAN. The Line below represents the Natural Length of 



the Animal 



(Eeduced from a Figure, in 8. I. Smith's Eeport, of Fresh-Water Crustacea, published by U. 



S. Fish Commission.) 



