140 EXPLANATION OF ITS HABIT. 



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 particulars like 

 that of an Actinia, surrounded by a delicate 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 peregrina- 

 tions 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 Mollusk] 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 

 is 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 se- 

 lect as its support the inner lip of some univalve 

 shell, having adhered to which, the lateral expansions 

 creep along the shell, following its surface until they 



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



