3 o2 ECHINODERMS. 



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 larvae 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 Hystricriniis from the 



