218 



HOMOLOGIES. 



ponderance of the ab-oral region determines all 

 that peculiarity of form which distinguishes them 

 from the other Echinoderms, while the oral region 

 is comparatively insignificant. The ab-oral region 

 in the Crinoid rises to form a sort of cup-like 

 or calyx-like projection. The plates forming it, 

 which in the Star-Fish or the Sea-Urchin are 

 movable, are soldered together so as to be per- 



Crinoicl with branching crown ; oral side turned upward. 



fectly immovable in the Crinoid. Let this seem- 

 ing calyx be now prolonged into a stem, and we 



