TEN-LEGGED CRUSTACEA 



421 



not easily approached by its enemies. The anemone, in its turn, finds 

 a most profitable situation upon the mollusc shell, for in the first place 

 it picks up many a morsel which falls from the table of its host, and, 

 secondly, from its place of settlement it participates in the constant 



9. 



E.i. 



E.J. 



Maeine Ci;ustai:ea in the Aquarium. 

 E. , Hermit crabs in the shells of whelks (about one-half natural size) ; E.I., shown in 

 creeping attitude ; two specimens of a sea-anemone (Adamsia rondcletii), Sr., have 

 settled on the shell, one with tentacles expanded, the other with the same retracted ; 

 E.2., hermit crab leaving the mollusc shell, which has become too small, in order to migrate 

 to a larger one ; E.3., hermit crab withdrawn inside shell ; on the shell of the whelk are 

 shown a few ''acorn shells" (Balanus, see p. 420), with their "cirri" partly extended; 

 K., Woolly crab (Dromia vulgaris), holding over its back, by the claws of the two last 

 legs, a living sponge (Suberites) (about one-half natural size) ; Sg. , common shrimps (the 

 largest about one-half natural size) ; G. , a prawn (about three-fourths natural size). 



migrations performed by its host in search of food, and is therefore itself 

 able to obtain much richer spoil than if it remained fixed upon its rock 

 and compelled to wait for what food chance conveyed to it. We have 

 here, therefore, an instance of the " commensalism " of two entirely 



28—2 



