EB Billings on the structure of the Crinoidea, etc. 57 
the column of an Actinocrinus is the homologue of that of Pen- 
tacrinus caput Meduse. 
n an important paper entitled ‘“ Remarks on the Blastoidea, 
with descriptions of New Species” which Meek and Worthen 
have kindly sent me, the authors, in their comments upon my 
views, state that :-— 
Curves between the mouth and the anus. It fills only a small 
part of the cavity of the body, the remainder being occupied 
mostly by the chylaqueous fluid, which is constantly in motion 
and undergoing seration, through the agency of various organs, 
such as the respiratory tree and branchial cirrhi of the Holo- 
thuridea, the dorsal tubuli of the Asteride and the ambulacral 
Systems of canals of the class generally. In no division of the 
animal kingdom do the respiratory organs ies 22 a larger pro-- 
te wa : 
Professor W yville Thomson says that inside of the cavity of 
the stomach of’ the recent Crinoid, Antedon rosaceus, t a 
: 
Ses that the convoluted plate may represent this organ. 
present I think it does not. | 
I believe that the reason why the convoluted plate attained 
