NO. 1846. ON CERTAIN ELEUTHEROZOIC PELMATOZOA— KIRK. 123 



temporarily anchoring the crinoid. It was suggested b}?- de Loriol 

 (1878, p. 12) that the cirri were used as organs of locomotion, a sup- 

 position that may in part be right, as is elsewhere indicated. The 

 development of these cirri even in Paleozoic times is most note- 

 worthy. For example, in Cordylocrinus, and particularly in a new 

 Camerate genus from the Hamilton a most extraordinary develop- 

 ment of cirri is to be noted. In some cases these cirri reach from 

 vvell down on the column to considerably above the tips of the arms, 

 the total length being two to three times the total height of the 

 crown. In both of these genera, and particularly in Cordylocrinus, 

 the crown is frequently so completely covered Iw cirri as scarcely to 

 be visible. As has been noted under Cordylocrinus, the columns are 

 remarkably short, measuring but a few inches in length, and show no 

 signs of permanent fixation. 



In connection with the formation of cirri as induced by an eleu- 

 therozoic habit should be recalled the grapnel of Ancyrocrinus , the 

 float of Scyyliocrinus, and the distal knobs of certain Devonian 

 C^amerata. The float of ScypJiocrinus is unique and is a type of 

 modification scarcely to be looked for. The distal excrescences, and 

 the grapnel of Ancyrocrinus are obviously for the purpose of bal- 

 ancing the crinoids, as no doubt is the fused distal portion of the 

 LepadtOcrinus column. 



It is a noteworthy fact that among the Crinoidea, especially in 

 the later forms, tlie stem is frequently lost, or but a remnant of it 

 remains. Among the Cystidea this is never the case. The reason for 

 this is obvious. In the latter group the column has not become so 

 higlily differentiated an organ as among the Crinoidea and Blastoidea. 

 It still contained a portion of the visceral mass, in all probability, 

 and could not readily be shed. Again, the stem had not become so 

 higlily specialized for purposes of attachment that it could not be 

 modified so as be made a useful adjunct in the propulsion of the 

 animal. 



Effect of a detached mode of life on the arms. — The tendency toward 

 more perfect freedom — that is, toward directed movement — would of 

 necessity find expression in a strengthening of the arms and their 

 more perfect adaptation as swimming organs. Concomitant with 

 such modification and induced by the mechanical influence of the 

 arm-action may be noted a modification of the tegmen, both as to 

 composition and orientation. These features are of indifferent 

 value in many cases, no doubt, owing to the variable degree in wluch 

 freedom was assumed, probably even within a closely circumscribed 

 group. Under such circumstances the influence of a given type of 

 life, held for short or variable periods, has to contend with cumu- 

 lative tendencies induced by a diametrically opposed form of life held 

 for the greater part of the lives of the common stock. Moreover, 



