8 CORALS AND CORAL LSLANDS. 



published by Prof. Verrill ; the specimen was collected by 

 the Zoologist, Dr. W. Stimpson. As Prof. Verrill states, 

 the Dorippe carries, for its protection when young, a small 

 shell over its back, which it holds in this position by means of 

 its two reversed pairs of hind legs. The Actinia appears to 

 have fixed itself, when young, to the shell, and afterwards, by 

 its growth, spread over the back of the crab, taking the place 

 of the shell. 



This case of commensalism, like most others, is not a mere 

 chance association of species, for the two always go together, 

 the Actinia, according to Dr. Stimpson, never being seen 

 except upon the crab's back, and the crab never without its 

 Actinia. The fact shows an instinctive liking on the part of 

 the Actinia for a Dorippe courser, and for the roving life thus 

 afforded it. And the crab is undoubtedly conscious that he is 

 carrying his fortress about with him. It is not a solitary case ; 

 for there are many others of Actiniae attaching themselves to 

 locomotives — to the claws or backs of crabs, or to shells in 

 possession of soldier crabs, or to a Medusa ; and frequently 

 each Actinia has its special favourite, proving an inherited 

 instinctive preference for rapid change of place, and for just 

 that kind of change, or range of conditions, which the pre- 

 ferred commensal provides. Prof. Verrill has an interesting 

 article on this subject, with especial reference to crustaceans, 

 in the third volume of the Aino'ican Naturalist. 



Species living in sand are often unattached ; and then the 

 base is rounded or tapering, and sometimes balloon-shaped ; 

 some of them are long and almost worm-like, and even burrow 

 like worms. 



The following are figures of three species : one, figure 3, 

 exhibiting simply the tentacles and disk of the Actinia, the 

 only parts visible above the sand ; the others showing the 

 whole body removed from the sand, and consequently a little 

 out of shape. They are from Gosse's " British Sea-Anemones," 

 in which they are given with the natural colours. Figure i re- 

 presents the Peachia hastata of Gosse, a beautiful species hav- 

 ing twelve large tentacles; figure 2 the Edwardsia callvnorpha 



