3S DK. P. H, CAEPENTEB ON CERTAIN POINTS 



' Challenger' Crinoids *, he will find that our views are identical, 

 and not divergent as he states. I freely admit that Bury thinks it 

 probable that the oculars of an Urchin are terminals and that the 

 primary radials are unrepresented t. But the occasional entrance 

 of the oculars into the basal ring, and the resemblance of TiarecM- 

 iius to a Blastoid J, are small difficulties in the way of accepting 

 this view without the strong proofs which will, I hope, soon be 

 forthcoming. It may be that the primary abactinal radials are not 

 developed in the Urchins any more than tlie infrabasals are. But 

 if the plates hitherto regarded as such should really prove to 

 belong to the left antimer, another piece of evidence will be 

 afforded in favour of the view that the ancestral Echinoderm had 

 radial as well as interradial plates developed on the actinal hemi- 

 some, in relation with its left body-cavity. 



It may be noted, too, that Bury's observations on Echinoderm 

 larvse answer many of the objections brought forward by the late 

 Professor Neumayr against the views of those who believe the 

 apical system of all Ecliiuoderms to be constructed upon a common 

 plan, modified though it be to a very considerable extent among 

 the diflerent members of the group. Neumayr attacked the 

 subject with very great skill, but almost entirely from the jjalaeon- 

 tological side ; and I do not think that he gave due consideration 

 to the e\'idence either of embryology or of comparative anatomy. 



To discuss his arguments in detail would be impossible now ; 

 but I hope to do so at some future time, when I shall also pro- 

 pose to consider the varying theories of Semon and the Sarasins, 

 of Stlirtz and "Walther respecting the phylogeny and mutual 

 relationships of the diiferent Echinoderm classes. One point, 

 however, and that a fundamental one, I cannot pass without notice. 



Neumayr stated § that " von der richtigen Deutung des See- 

 igelscheitels hangt zum grossen Theile das richtige Verstandniss 

 der gauzen Entwicklung der Echinodermen ab, und ganz speciell 

 ist hiebei das Verhaltniss der Grenital- und Ocellartafelchen 

 zueinander von grosster Bedeutung." Taking as a starting- 



* Op. cit. pp. 393-402. 



t Quart. Journ. Micr. Sci. 1889, toI. xxix. p. 442. Bury's view lias been 

 adopted quite recently by Janet and Cuenot (" Note sur les Orifices Genitaux 

 multiples," &c., Bull. Soc. Geol. France, tome xix. p. 303. 



I If it be a valid argument that the oculars of an Urchin are terminals and 

 not radials, because of their relation to the ambulacra, it is equally applicable to 

 the radial plates of a Blastoid, which are universally accepted as homologous 

 with those of a Crinoid. § Oj:). cit. p. 363. 



