440 THE CANADIAN NATURALIST. [Dec. 



rectly described and delineated by Volborth and Joh. Muller. 

 Close to this is seen the other l orifice,' viz., the external genital 

 organ. All specimens that I have examined have this so-termed 

 ' orifice' in such a condition that it most likely is the remnant 

 of a prominent broken part, and it must be assumed that in this 

 species also it had a conical form, but remained mainly in the 

 surrounding stone-matrix. Volborth's figure (Ueber die Russis- 

 chen Sphaeroniten, x. ix. f. 9) appears to be correct, but gives no 

 complete evidence as to the presence of the three valves. That 

 the ' pyramid,' which in Leskia is the armature and covering of 

 the mouth, is the same thing in Cystidea, is now quite certain ; 

 in the last-named group it was, doubtless, also the vent. The 

 mouth does not lie where J. Muller and Yolborth sought for it, 

 viz., in the centre of the ambulacral furrows ; and the organ, inter- 

 preted as the vent by Volborth and Yon Bueh, is more correctly 

 regarded as an external sexual organ." 



It is not my intention to criticise the various interpretations of 

 the morphology of Cystidea given by different authors, or to 

 trespass on the space here allowed me by a detailed examination 

 of all the questions entangled with them. But should I venture 

 to express any humble opinion of my own on this important point 

 in the morphology of Echinodermata, I must first confess that 

 hitherto I have been very sceptical as to the theory advocated so 

 very ingeniously by Mr. Billings and now upheld by Mr. Loven. 

 The concordance between these two authorities is nevertheless 

 not so great as would be supposed — that the ' pyramid' was the 

 mouth of the Cystidea, and that this orifice accordingly would 

 lie elsewhere than in the centre of the ambulacral system, where 

 it lies in all living Echinoderms and (I may add, where it did lie, 

 I have no doubt, also in the Palaeozoic Crinoids, where no super- 

 ficial ambulacral channels are to be seen, but where they pursued 

 their way on the inferior surface of the 'vault' through the 

 1 ambulacral orifices' at the base of the arms, — as shown by 

 Mr. Billings, with those researches (see Decades Geol. Survey of 

 Canada) I was, I regret, unacquainted when I wrote my paper 

 on Pentacrinus, etc.) I know no other exception to this rule; 

 and would it not be a dangerous thing — not to be done without very 

 strong arguments — to give up the leading principle of Palaeonto- 

 logy, viz., that only from the organization of the living form can 

 we learn to understand that of the extinct ? Might we not thus 

 too often run the risk of giving up ourselves to the delusions of 



