380 Mr. C. Wachsmuth on the Internal and 
the most perplexing points in the investigation of the structure 
of Paleozoic Crinoids. In all Radiates (even of the most 
inferior groups) this organ is located invariably at one end of 
the vertical axis, although that axis or centre is not always 
the centre of figure. It occupies in the recent Crinoids the 
upper end of this axis; but in many at least of the Paleozoic 
Crinoids, the portion of the summit where, from analogy, we 
should expect to find the oral aperture is perfectly covered by 
solid and immovable plates. The only aperture in connexion 
with the visceral cavity is lateral or subcentral, placed out- 
side of the radiation and within the interradial area, where, 
from analogy, we must expect to find the anus. If, as Mr. 
Billings*, Dr. Whitey, and the older writers on Crinoids sup- 
posed, this aperture served both as mouth and vent, so that 
these Crinoids took in their food through the anus, this stands 
as the sole exception to the rule governing the class. It is 
-true the Ophiurans, for instance, have no separate anal 
opening, and the same aperture performs both oral and anal 
functions ; but it is placed within the radial centre, and there- 
fore cannot be homologized with the interradial orifice of 
Paleozoic Crinoids. In Antedon rosaceus, although the nas- 
cent Crinoid develops already within the pseudembryo a 
separate mouth and vent, a single orifice serves for some time 
both as oral and anal aperture ; yet it is the permanent mouth, 
occupying the centre of the ambulacral system}. While we 
thus find the mouth performing permanently or temporarily 
anal functions, we have on the other hand no evidence, either 
from recent nature or from embryology, that an anus ever 
becomes developed into, or performs the office of, a mouth. 
The Crinoids of our present seas live exclusively on micro- 
scopic food; and we must expect to find that the Paleozoic 
Crinoids subsisted upon very similar food and had a very 
similar mode of alimentation. Whenever in Antedon alimen- 
tary particles fall upon the furrows of the arms or pinnule, 
they are transmitted downward along these furrows to the 
mouth wherein the furrows terminate. Dr. Carpenter remarks 
on this subject § :— 
“The transmission of alimentary particles along the ambu- 
lacral furrows is the result of the action of cilia with which 
their surface is clothed. Although I have not myself suc- 
* Silliman’s Journ. 1869, vol. xlviii. no. 142, p. 69. 
+ Journ. Nat. Hist. Boston, 1862, vol. vii. no. 4, p. 481. 
{ Sir Wyville Thomson, Phil. Trans. of the Royal Society. 
§ “Researches on the Structure, Physiology, and Development of Ante- 
don rosaceus.—Part I.,” by W. B. Carpenter, M.D., F.R.S. (Phil. Trans. 
Roy. Soe. vol. clvi. part 2, 1866). 
