13 2 A. Alcock — NeiD and Bare Species of Crtistacea. [No. 2, 



in coral ; and I have myself seen a large Coenohita, on the island of 

 Minnikoy, holding the empty shell of a small coco-nut over its 

 abdomen. Again, in other parts of the world, Gryllopagiirus lives in 

 burrows of its own construction ; Pylocheles AgassizU was found con- 

 cealed in a cavity in a piece of sandstone, and another specimen was 

 taken from the gastral chamber of a siliceous sponge ; Xylopagurus 

 rectus, like oar Pylocheles Miersi, was discovered in a lodgings in drift 

 wood ; Ostraconotus and Tylaspis are both believed to have some special 

 protective shield, other than a shell : and Porcellanopagurus lives free 

 among sea-weed. 



Again, the association of our new form of Hermit-crab with a sea- 

 anemone is nothing strange : indeed, commensalism between Crustacea 

 and sea-anemones is one of the most familiar facts of zoology, and a 

 large number of instances of it have been described. In most cases, 

 however, the facts seem to be that an individual of a definite species of 

 crab and an individual of a definite species of sea-anemone have both 

 at once taken possession of the same mollusk-shell, which they continua 

 to inhabit for their mutual advantage, — the crab acting as locomotive to 

 the sea-anemone, and the sea-anemone in return acting as a defence and 

 warning-post, and possibly also as a decoy, for the benefit of the crab. 



But though the mutual advantage of the association is plain 

 enough, the absolute and essential necessity of it is not so plainly seen, 

 and it is reasonable to imagine that when in the course of growth the 

 Hermit-crab has to seek a new and larger shell, the partnership with 

 the sea-anemone can be dissolved by simple withdrawal, without dan- 

 gerously afiecting the life of either individual — at any rate until such 

 time as each can find a new partner of suitable size. In other words^ 

 there is no adaptation of either animal to the other, and each seems 

 capable of existing apart from the other. 



In the present case there is no shell to act as introduction to and 

 bond between the two animals ; and the sea-anemone, which is a colonial 

 form with a spreading coenosarc, merely forms a sheet, which the crab 

 simply tucks under its telson by one end and pulls over its back by 

 the other end — the polyps seeming to have no power of adhesion and 

 to depend on the crab for a fast hold. 



The nearest approach to this state of affairs is found in Parapagu- 

 rus pilosimauus, which, wh»n full-grown, lives in a cavity hollowed out 

 of the coenosarc of a colony of a large species of JEpizoanthus. But 

 in this case the individual hermit-crab and sea-anemone start their 

 partnership with an empty mollusk-shell, which in course of time, a& 

 the occupants increase in size, becomes absorbed, so that, at last, 

 the crab is entirely dependent on the polyp- colony for the protection of 

 its soft abdomen. 



