3° 2 
E CHINODERMS. 
tion ; those near the extremity of the arm being specially active. If its extremity 
be touched by any irritating substance, the arm is erected at right angles to the 
upper surface of the animal and so removed from the other arms, while the pinnules 
move something like the legs of a fly that is cleaning itself. If, however, this 
proves ineffectual, the arm bends over to the one on the opposite side, the pinnules 
of which then assist in the operation. The pinnules move in this manner to dis¬ 
embarrass the arm of fragments of foreign matter that are too large; but the 
hooks at the end of the pinnules can catch and retain minute fragments, which, as 
they decay, attract animalcule, and so furnish food for the animal. If a stimulus 
be applied to any point on the under surface of the animal, the arms on the side 
from which it comes are simultaneously and forcibly pressed down, apparently to 
create a current that shall wash away the irritant. If an arm be cut off, it will 
continue to move for a short time. The crinoid, however, flattens its remaining 
arms, and rests immovable for half a minute; it then slowly crawls in a direction 
away from the wound. Antedon does not appear to like the light, and if placed 
on the surface of a stone in a glass vessel, always prefers to crawl to the under 
side, where it remains fixed by its cirri. If, however, a strong light be reflected 
on to the under side of the stone, while the top is kept dark, the animal will crawl 
back to the top. It is by crawling that the crinoid usually moves from place to 
place. The arms on the side towards which it intends to move, are stretched out; 
the pinnules are curved backwards towards the body, like so many grappling-hooks; 
and the arms are then curved up in S-fashion, thus dragging the animal along. 
Meanwhile, the arms of the opposite side move in the converse way, and their 
pinnules are directed away from the body, so that they push instead of pull. 
At the present day crinoids live in all seas at depths between fifty and three 
thousand two hundred fathoms; but they prefer clear and undisturbed waters. 
The same has been the case in former geological periods, for while crinoids are 
abundant in limestones, of which their own remains form large masses, they are much 
rarer in sandstones and shales. As in the case of the well-known pear-encrinite, 
colonies of crinoids that lived in clear water have been suddenly overwhelmed by 
an influx of mud, which first killed and then preserved them. Unstalked as well 
as stalked crinoids live chiefly in colonies; but this is due less to sociability than 
to limited powers of motion even in the larval state. In the older rocks, 
individuals of many different genera and species may be found that lived in close 
association. In the later periods it is more usual to find numerous individuals of 
the same species in association; examples of such colonies among stalked crinoids 
are Rhizocrinus in the North Sea and off North America, Bathycrinus in the 
Southern Ocean, Pentacrinus off Portugal and in the Caribbean Sea, and 
Extracrinus in the Lias of Lyme-Regis. 
The food of crinoids consists chiefly of foraminifera, diatoms, and the adults 
of small and the larvm of larger crustaceans. Crinoids themselves form food 
for fish, though nowadays their place seems to be taken by the brittle-stars and an 
occasional sea-urchin. As protection against such attacks, some crinoids have 
been provided with spines, either as movable processes from the plates of the 
test, as in Dorycrinus from the Carboniferous of North America, or, very rarely, 
movably attached like the spines of a sea-urchin, as in Hystricrinus from the 
