574 



ZOOLOGY 



SECT. 





FIG. 473. Scyllarus arctus. 



ant.l, antennule ; ant.2, antenna ; 

 E, eye. (After Cuvier.) 



sterna, the antennae (ant. 2} short 

 anc [ plate-like, and the eye-stalks (E) 

 enclosed in socket-like grooves of 

 the carapace. Most of these charac- 

 ters show an approximation to what 

 is found in the Crabs. 



Of the Anomura, the Hermit- 

 Crabs (Pagurus, &c., Fig. 474) are 

 very strangely modified in relation 

 with their peculiar mode of life. 

 They are always found inhabiting 

 the empty shells of Gastropods 

 (Whelks, Periwinkles, &c.), the 

 abdomen, which has become spirally 

 twisted, completely enclosed within 

 the shell and only the cephalothorax 

 protruding. In correspondence with 

 this mode of protection, the abdo- 

 men is soft, having only vestiges 

 of terga (t) on the dorsal side, and 



its appendages are more or less atrophied except the sixth 



pair (up), which take the form of a pair of hooks, and are 



used to hold on to 



the columella of 



the shell. The fifth 



pair of legs (1.5) 



are much reduced, 



and in some species 



one of the chelipeds 



is greatly enlarged 



and its chela (ch) 



acts as an oper- 



culum, completely 



closing the mouth 



of the shell when 



the animal is re- 

 tracted, or both che- 

 lipeds are enlarged 



to perform this 



function. As the 



Hermit-Crab grows 



it takes up its abode 



in larger and larger 



shells, sometimes 



killing and remov- 

 ing piecemeal the FIG. 474. Pagurus bernhardus. ch. clu-la .>r 



^^ rigllfc leg ; '*' L5 > fourth :llul mth '*'-- < 

 t> abdominal terga ; up. uropocls. (After Bell.) 



I.* 



