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 perfectly immovable in the Crinoid. Let this
seeming calyx be now prolonged into a stem, and we see at once how
striking is the resemblance to a flower; turn it downwards, an attitude
which is natural to these Crinoids, and the likeness to a drooping
lily is still more remarkable The oral region, with the radiating
ambulacra, is now limited to the small flat area opposite the juncture
of the stem with the calyx; and whether it stretches out to form long
arms, or is more compact, so as to close the calyx like a cup, it
seems in either case to form a flower-like crown. In these groups of
Echinoderms the interambulacral plates are absent; there are no rows
of plates of a different kind alternating with the ambulacral ones, as
in the Sea-Urchins and the Star-Fishes, but the ab-oral region closes
immediately upon the ambulacra.
It seems a contradiction to say, that, though these Crinoids were the
only representatives of their Class in the early geological ages,
while it includes five Orders at the present time, Echinoderms were as
numerous and various then as now.
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