ETJPAGTJIUTS. 557 



makes the possession of a full-sized shell of secondary 

 importance. The young E. bernhardus is able to select 

 from a large number of species. I have found specimens 

 commonly in the following, but they use almost any 

 shell or hollow object of suitable size and shape. 



Buccinum undatum Littorina littorea. 



(young). Dentalium entale (rarely). 



Fusus antiquus (young). Purpura lapillus. 



Murex erinaceus (young). Trochus cinerarius. 



Natica nitida. Nassa incrassata. 



N. monilifera. Turritella communis. 



Biology of the Shell. 



The possession of a shell is a matter of importance 

 to the hermit crab, not solely for its protective value, 

 but also because it seems to concern its health. Although 

 crabs may be kept naked for a considerable time if they 

 are solitary and in suitably inoffensive surroundings, 

 they weaken in time and eventually die. To keep them 

 without covering in company, or with rough and jagged 

 surroundings, is rapidly fatal, as the delicate abdomen 

 is very easily ruptured, and death invariably follows. 

 M. T. Thompson has experimentally studied the effect 

 of the shell on the metamorphosis, with valuable results. 

 His conclusion is: "The stimulus of a shell is not 

 necessary for the completion of the metamorphosis any 

 more than for its inauguration," but the change from 

 the Glaucothoe to the adult is delayed on the average 

 by the absence of a shell, and the health of the larva 

 is deeply affected. His experiments on naked larvae 

 show most distressing mortality. The shape and nature 

 of the covering seems to matter little, either in respect 

 of form or health, so long as one is present. 



