444 THE CANADIAN NATURALIST. [Dec. 



The principal office of the arms of the existing Crinoids is the 

 maturing of the ova. On comparing the arms of the extinct 

 Crinoids with those of the species living at the present day, we 

 find that both have the same anatomical structure and, con- 

 sequently, they are all the homologues of each other. The small 

 apertures, at the bases of the arms of the ancient species, are the 

 passages through which the ovarian tubes and the vessels of the 

 ambulacral system gained access to the grooves and pinnulae. 

 Their functions were first pointed out in my Decade. The arms 

 of the Cystidea are the homologues of those of the Crinoids. 

 This at once proves that, in the Cystidea, the orifice at the apex, 

 which in all cases opens out into the grooves of the arms, is the 

 ovarian aperture. The large lateral orifice is undoubtedly the 

 exact homologue of the valvular opening in the summit of 

 Caryocrinus which is admitted by all to be the mouth. I 

 proved all this in my Decade, and consequently in 1858, the 

 date of the publication of that work, the theory that the lateral 

 aperture of the Cystidea is the mouth, ceased to be a mere 

 hypothetical supposition as Dr. Liitken calls it. 



The Cystideans are rare fossils ; few Palaeontologists have 

 occasion to examine them, and consequently only a few have given 

 their opinion on this vexed question since 1858. J. W. Salter, the 

 celebrated English Palaeontologist says : "I strongly suspect Mr. 

 E. Billings is right ; this is the anal, not the ovarian Pyramid,"* 

 thus partly adopting my views. Prof. Wyville Thompson also 

 agrees with me that it is not the ovarian orifice, but then he 

 strongly opposes me in the view that it is the mouth on 

 the same ground, that is alluded to by Dr. Liitken, i.e., that 

 it is not situated in the centre of the radial system. f Prof. 

 J. D. Dana has recognised it as the homologue of the oral 

 and anal aperture of the Criniods, which is exactly the opinion 

 advocated in my Decade^ ; and now it gives me much satisfaction 

 to add the illustrious name of Prof. S. Loven to this short 

 list. 



With regard to the grounds taken by Prof. Wyville Thompson 

 and Dr. Liitken, I freely admit that if it is impossible for an 

 Echinoderm to have the mouth situated anywhere except in the 



* Memoirs ot the Geological Survey of England, vol. iii, p. 286. 

 t Edinburgh New. Phil. Jour. vol. xiii p. 112. 

 \ Manual of Geology p. 162. 



