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 

 Comatulae 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 



