THE STONE LILIES OR CRINOIDS 3269 



nervous system that has its headquarters at the bottom of the cup. This swimming 

 has been observed in both Antedon and Actinometra kept in an aquarium. As a 

 rule, however, these animals remain attached by their cirri to rocks, to the bottom 

 ooze, to seaweeds, or to other marine animals. In this position the arms are out- 

 spread, and the small branches or pinnules that line their sides are kept slightly 

 waving. If the water be ruffled, the first impulse of the crinoid is to flatten its 

 arms out suddenly and to hold on to the rock or other object with its pinnules. 

 The pinnules of an Antedon can be bent in any direction; 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 oper- 

 ation. The pinnules move in this manner to disembarrass 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 animalculae, and so fur- 

 nish 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 cri- 

 noid, however, flattens ita 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 sideof 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 toward which it intends to move, are 

 stretched out; the pinnules are curved backward toward 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 abun- 

 dant 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, colo- 

 nies 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 at Ivyme-Regis. 



