EXPLANATION OF ITS HABIT. 133 



is delicately wliite, dotted over with round spots of 

 rosy piu'ple. I have said it adheres around the shell- 

 mouth; and this is a curious circumstance, because, 

 as it does not extend across the orifice, the animal 

 assumes an annular form, the Crab inhabiting the 

 shell, and protruding freely through the opening. 

 On that side which is next the inner lip or column of 

 the shell, and beneath the breast of the Crab, there 

 opens a wide oblong mouth, in all essential parti- 

 culars like that of an Actinia, surrounded by a deli- 

 cate fringe of short white tentacles ; which in general 

 are freely exposed, seeking for prey ; the animal being 

 little alarmed by the rude treatment to which the 

 peregi-inations of its active companion expose it. 



This form, at first sight, seems so very anomalous, 

 that a naturalist of no small knowledge has recourse, 

 for its explanation, to the suggestion " that the old 

 shell [of a Gasteropod ^lollusk] with a young Crab 

 in it may have been swallowed by the Actinia ; that 

 the Crab may have forced its way through the walls 

 of the stomach and the integuments of the latter ; and 

 that the Actinia, then secreting a peculiar membrane 

 to defend its base, the Crab may have found itself 

 provided with a habitation suited to its wants." ^ 

 Yet it appears to me that the deviation from normal 

 structure is more apparent than real. The Adamsia 

 4s evidently an Actinia of a long-oval form, capable 

 -of development in its long diameter into two length- 

 ened wings. Its instinct invariably leads it to select 

 as its support the inner lip of some univalve shell ; 



* Coldstream, in Johnston's Brit. Zooph. i. 209. 



