THE CRINOIDEA. 



499 



strong elastic ligamentous fibres. The centre of each is 

 traversed bj a longitudinal axial canal, which extends 

 through the whole length of the stem and is occupied b^ a 



Fig. 14Q.— Fhizocrimis iQf'ofensis. (After Sars.) 



T. Ehizocrinus entire: a, enlarged upper joint of the stem ; b, larval joints of the 

 stem ; c, cirri ; d, brachia. 



II. Calyx and nrms, with tlie summit of the stem of a RMzocrin'us havinj; five well- 

 developed brachia : a, as before ; 5, first radials ; /•-, r^, second and third radials ; 

 6^ first bracliial ; 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 articuh of the distal 

 portion of the stem. 



The proximal joints become gradually shorter in propor- 

 tion to their length, until they assume a discoidai 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 enlargedj solid, pear-shaped ossicle, wliich is 

 probably formed by the coalescence of several articvli. Upon 



