ACTINILA 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 Actiniz 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 
g, and sometimes balloon-shaped ; 
base is rounded or tapering, 
some of them are long and almost worm-like, and even burrow 
hke 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 Peachia hastata of Gosse, a beautiful 
species having twelve large tentacles; fig. 2, the Adwardsia 
callimorpha.G.; fig. 83, Halocampa chrysanthellum 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 
