4io 



PELMAT0Z0A. 



tinal ") surface, with the mouth-opening, is turned upwards. In the 

 Free Crinoids, in which the adult is devoid of a peduncle of 

 attachment, the animal has it in its power to move about freely by 

 swimming ; while it can at the same time assume the position char- 

 acteristic of the Stalked Crinoids, since it can fix itself to foreign 

 objects with the mouth turned upwards and the dorsal surface 

 directed downwards. 



The " Feather-stars," as exemplified by the common Antedon 

 (Comatula) rosacea of British seas (fig. 284), belong to the group 

 of the " Free Crinoids," being attached by a stalk in their young 

 state only. The adult animal is free, and consists of a pentagonal 

 or cup-shaped body or " calyx," which gives origin on its sides to 

 five jointed processes or "arms."' The calyx encloses the visceral 

 mass or disc, the upper or " actinal " surface of which exhibits the 

 apertures of the mouth and anus. The five " arms " bifurcate 

 almost immediately after their origin from the calyx, so as to give 

 rise to ten long slender processes, which are transversely jointed, and 





Fig. 285. — Side-view of the calyx of Antedon sp., enlarged, the cirri being mostly removed, 

 and the bases of only two rays being shown, cd, Centrodorsal plate, with the origins of the 

 dorsal cirri (c) ; r, One of the " primary radials " ; sr, One of the " secondary radials " ; ar, One 

 of the "axillary radials," carrying the bifurcations of the arm; br, First "brachial" plate. 

 (Original.) 



are fringed on both sides by delicate filaments or " pinnulse." The 

 dorsal surface of the body carries a number of delicate jointed 

 flexible processes (figs. 284 and 285, c), which are attached to the 

 so-called " centrodorsal " plate, and are known as the " cirri." By 

 means of these the animal can moor itself temporarily to foreign 

 objects, with the mouth turned upwards. 



