400 THE VOYAGE OF H.M.S. CHALLENGER. 
clear that this structure cannot have been developed from the primary interradial 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 Lovén, render 
Perrier’s views respecting the development of the odontophores of an Asterias from the 
primary interradial 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, Lovén “a attribué & l’Oursin 
une position exactement inverse de sa position normale.”’ He regards an Urchin as a 
Crinoid with a large visceral mass to which the arms are fixed, as for example in 
Eucalyptocrinus ;” while “la bouche serait située au point d'insertion du disque sur 
la tige.” Under these circumstances the nervous system and ambulacral canals of an 
ce 
Urchin would have “exactement les mémes rapports que ceux qui nous sont offerts par 
la Comatule. 11 est & remarquer que précisément, en ce point, le calice de nombreux 
Crinoides pédonculés s’invagine, et présente des plaques qui ne sont pas sans analogie 
avee celles qui constituent la Janterne d’Aristote des Oursins et plus particulitrement 
des Clypéastres.” 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 
périprocte, mais bien les pieces constitutives de la lanterne d’Aristote. Quelque hardie 
que paraisse cette interprétation . .... . nous sommes persuadé que tout esprit non 
prévenu sera frappé de I’étroite ressemblance d'un Oursin régulier avec des Crinoides tels 
que le Calherinus et surtout les Eucalyptocrinus.” I fear that in this matter I 
cannot be said to have an “esprit non prévenu”; 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 types as Hucalyptocrinus 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 
Now. Archiv. du Mus. @ Hist. Nat., 2™° sér., 1884, t. vi. p. 161. 2 Comptes rendus, t. xcvill. p. 1450, 
Nouv. Archiv. du Mus, d’ Hist. Nat., 2m sér., 1884, t. vi. p. 161. 
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