THE CRINOIDEA. 



499 



strong elastic ligamentous fibres. The centre of each is 

 traversed by a longitudinal axial canal, which extends 

 through the whole length of the stem and is occupied by a 



Fig. \A5.—RMzocrinus Iqfotensis. (After Sars.) 



I. Rhizocrinus entire: a, enlarged upper joint of the stem ; 5, larval joints of the 

 stem ; c, cirri ; d, brachia. 



II. Calyx and arms, with the summit of the stem of a Rhizocrinus having five well- 

 developed brachia : a, as before ; s, first radials ; r 8 , r 3 , second and third radials ; 

 I/, first brachial ; p, p, pinnules. 



III. Upper part of the stem and oral face of the calyx, viewed obliquely: v, lower 

 part of visceral mass ; st, tentacular grooves ; 6, oral valves ; t, oral tentacles ; 

 an, anus. 



soft but solid substance. The distal joint of the stem is not 

 directly fixed to the surface to which the Crinoid is attached, 

 but is connected therewith by the branched cirri which pro- 

 ceed from it. Each cirrus has a skeleton composed of joints 

 or articuli, somewhat like those of the stem, and traversed by 

 a prolongation of the axial canal. Similar cirri are developed 

 from a larger or smaller number of the articuli of the distal 

 portion of the stem. 



The proximal joints become gradually shorter in propor- 

 tion to their length, until they assume a discoidal form. It 

 appears that new articuli are continually added at that end of 

 the stem which lies nearest the calyx. 



The summit of the stem, or the base of the calyx, is 

 formed by an enlarged, solid, pear-shaped ossicle, which is 

 probably formed by the coalescence of several articuli. Upon 



