400 THE VOYAGE OF H.M.S. CHALLENGER. 



clear that this structure cannot have been developed from the primary iuterradial plates 

 in the abactinal system of the larva ; for these last remain in the apical system, just as 

 they do in the Urchins. Sladen's observations, to say nothing of those of Loven, render 

 Perrier's views respecting the development of the odontophores of an Asterias from the 

 primary iuterradial plates round the dorsocentral of the larva, absolutely untenable, 

 and" one is therefore the less disposed to accept his statements concerning Brisinga, of 

 which no proof has yet been offered to his fellow-workers. 



In connection with this subject he has recently advanced some theories respecting 

 the mutual relations of a Crinoid and an Urchin which are altogether at variance with 

 those of most other naturalists, except perhaps Ludwig. He thinks that in comparing 

 the apical system of an Urchin with the calyx of a Crinoid, Loven " a attribue a I'Oursin 

 une position exactement inverse de sa position normale." ' He regards an Urchin as a 

 Crinoid with a lai'ge visceral mass to which the arms are fixed, as for example in 

 Eucahjptocrinus;'^ while "la bouche serait situee au point d'insertion du disque sur 

 la tige." Under these circumstances the nervous system and ambulacral canals of an 

 Urchin would have " exactement les memes rapports c|ue ceux qui nous sout offerts par 

 la Comatule. 11 est a remarquer que prdcisement, en ce point, le calice de nombreux 

 Crinoides pedoncules s'invagine, et prdsente des plaques qui ne sont pas sans analogic 

 avec celles qui constituent la lanterne d'Aristote des Oursins et plus particulierement 

 des Clypeastres." This idea has since been further developed.^ The arms of a Crinoid 

 grow at their free end, while the new ambulacral plates of an Urchin are formed round 

 the periproct. The base of the ambulacra is thus in the peristome. "Mais alors les 

 pieces homologues des plaques calicinales des Crinoides sont non pas les dix plaques du 

 periprocte, mais bien les pieces constitutives de la lanterne d'Aristote. Quelque bardie 



que paraisse cette interpretation nous sommes persuade que tout esprit non 



prevenu sera frappd de I'etroite ressemblance d'un Oursin regulier avec des Crinoides tels 

 que le Callicriims et surtout les Eucalyptocrinus." I fear that in this matter I 

 cannot be said to have an " esprit non prevenu " ; but it certainly appears to me 

 somewhat rash to attempt to overthrow the generally accepted ideas respecting the 

 mutual relations of an Urchin and a Crinoid by reference to such very highly 

 specialised t}'pes as Eucalyptocrinus and Callicrinus. Both in this respect and in the 

 comparison of the Crinoidal calyx to the lantern of Aristotle, I cannot help feeling 

 that Prof. Perrier has altogether lost sight of the embryological arguments by 

 which questions of homology are generally decided. The calyx of a Crinoid and the 

 apical system of an Urchin or Starfish have precisely the same relations to the vaso- 

 peritoneal apparatus of the larval Echinoderm ; and until some better reason can be 

 adduced for disregarding this relation than a more or less uncertain resemblance between 



' Nouv. Archiv. du Mus. (THist. Nat, 2""= ser., 1884, t. vi. p. 161. - Comptes rendus, t. xcviii. p. 1450. 



3 XoHV. Archiv. da Mus. d'Hist. Nat., 2°>« ser., 1884, t. vi. p. 161. 



