HOMOLOGIES. 223 
among them. Since I have become intimate with 
their wonderful complications, I have sometimes 
amused myself with anticipating some new vari- 
ation of the theme, by the introduction of some 
undescribed structural complication, and then 
seeking for it among the specimens at my com- 
mand, I have rarely failed to find it in one or 
other of these ever-changing forms. 
The modern Crinoid without stem, or the 
Comatula, though agreeing with the ancient in 
all the essential elements of structure, differs 
from it in some specific features. It drops its 
stem when full grown, though the ab-oral region 
still remains the predominant part of the body, 
and retains its cup-like or calyx-like form. The 
Comatule are not abundant,.and though repre- 
sented by a number of Species, yet the type as it 
exists at present is meagre, in comparison to its 
richness in former times. Indeed, this group of 
Echinoderms, which, in the earliest periods, was 
the exponent of all its kind, has dwindled grad- 
ually, in proportion as other representatives of 
the Class have come in; and there exists only 
one species now, the Pentacrinus of the West 
Indies, which retains its stem in its adult condi- 
tion. It is a singular fact, to which I have before 
alluded, and which would seem to have especial 
reference to the maintenance of the same numeric 
proportions in all times, that, while a Class is 
