CRINOIDEA 655 



the convex aboral side, the calyx bears in the middle a knob, formed 

 by the centrodorsal ossicle, which is the stump of the stalk and is 

 fringed with numerous slender, jointed cirri, each ending in a small 

 hooked claw and used for temporary attachment. 



The flat top of the calyx is covered with a leathery tegmen, in the 

 middle of which is the mouth, while the anal papilla stands in one of 

 the interradii. Five amhulacral grooves start from the mouth, where 



'd^ra-n. 



cir. 



cir.g. 



Fig. 459. A transverse section through the disc and base of an arm of An- 

 tedon rosacea. After Ludwig. at. various sections of alimentar^^ canal ; ax.coe. 

 axial part of perivisceral coelom, free from trabeculae; Br^, Br-, first and 

 second brachial plates; CD. centrodorsal piece; ch.on. "chambered organ" 

 in centre of aboral nervous system ; cir. cirri ; cir.g. branches of chambered 

 organ and genital stolon in cirri; coe. coelomic canals of arm; d.ra.n. radial 

 nerve of aboral nervous system; epm. epithelium of ambulacral groove; 

 g.sto. genital stolon; M. mouth; m. muscles connecting radial and brachial 

 plates ; n. nervous layer of ambulacral groove ; or.zvv. circumoral water vas- 

 cular ring, giving off, on the left in the figure, a canal to one of the tube feet 

 around the mouth ; por. pore canals ; R^, R^, R^, first, second and third radial 

 plates ; ra.wv. radial water canal ; stc. stone canals ; trb. trabeculae traversing 

 the coelom. 



they are separated by five low triangular flaps, the oral valves, and 

 radiate across the tegmen, each running to one of the pairs of arms, 

 to supply which it bifurcates. The groove on each arm gives a branch 

 to each pinnule. Along their whole course the grooves bear a row of 

 finger-shaped podia on each side, and they and the podia are ciliated. 

 Down this system a current set up by the cilia conveys particles 



