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- 
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Crinoid 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 
