ECHINODERMATA. 



273 



Meduste (Fig. 107), and Pentaerinus Europseus (Fig. 108). These 

 curious zoophytes resemble a flower borne upon a stem, which ter- 

 minates in an organ called the calyx, but which is, properly speaking, 

 the head of the animal. Arms, more or less branching, spring from 



Fig. 108. Pentaerinus Europteus (Thompson). 



this calyx, their ramifications, so formed, consisting of many pieces 

 articulated to each other. The calyx is supported by a stem, varying 

 in height, formed of pieces secreted by the living tissues which surround 

 them. The articulations of this stem are usually very numerous, 



T 



