ACTINIAE AND OTHER ACTINOID POLYPS. 25 



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 soli- 

 tary case ; for there are many others of Actinias 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 favorite, proving an 

 inherited instinctive preference for rapid change of place, and 

 for just that kind of change, or range of conditions, which the 

 preferred commensal provides. Prof. Verrill has an interest- 

 ing article on this subject, with especial reference to crustace- 

 ans, in the third volume of the American 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- Anem- 

 ones," in which they are given with the natural colors. 

 Figure 1 represents the JPeachia hastata of Gosse, a beautiful 

 species having twelve large tentacles ; fig. 2, the Edwardsia 

 callimorpha G. ; fig. 3, Halocampa chrysanthettum G-. Most 

 of these sand-dwellers bury themselves like the Halocampa, 

 and often hide all the disk but the mouth. The Edwardsia 

 is peculiar in having, above the hollow bladder-like basal 

 portion, a firm opaque exterior to the body, making for it 



