REPOKT ON THE ASTEROIDEA. 1^1 



and an infero-marginal series) will be found to exist. There is distinctly a double 

 row in Ctenodiscus. 



The young form of Porcellanaster from Station 137, described on a succeeding page 

 (p. 145), presents in such a remarkable manner all the characters mentioned by Perrier 

 as characterising Caulaster (excepting only the single row of marginal plates ascribed to 

 Caulaster, in my opinion with doubtful accuracy), that I cannot any longer believe that 

 the two forms belong to different genera. If my assumption is correct Caulaster as a 

 generic name must obviously give place to Porcellanaster. 



If my opinion that Caulaster is in reality a young Porcellanaster be correct, or if I 

 read the statements concerning that form rightly, the homology which Perrier has sought 

 to establish between, what he calls, the " pekloncule dorsal " of that starfish and the 

 stem of a Crinoid has no morphological basis whatever. The so-called dorsal peduncle seems 

 to me to be nothing more or less than an extraordinarily developed anal funnel (whether 

 aborted in function or not is immaterial for the present argument), and as such it is 

 the homologue of the anal funnel of a Crinoid. According to my views of Echinoderm 

 morphology it could not possibly be the homologue of the stem of a Crinoid, because 

 the dorso-central plate still exists independently in Porcellanaster, and clearly also in the 

 so-called Caulaster, according to Perrier ; and, in my opinion, it is with this plate alone 

 that any relationship with the stem of a Crinoid could exist in the apical system of 

 an Asterid. Furthermore, the "pe"doncule dorsal" of Porcellanaster and Caulaster is 

 excentric in position and situated at the side of the dorso-central plate, as is invariably 

 the case with the periproct in all larval Asterids in which we have been able to 

 observe the primative apical plates. If therefore the assumption that the "pe'doncule 

 dorsal " of Caulaster is the homologue of the stem of a Crinoid be admitted, it 

 follows logically that the anal aperture or periproct of all Asterids must be regarded 

 as the homologue of the stem in a Crinoid ; and it will impose upon those who accept 

 this view the task of indicating a new and rational homology for the dorso-central 

 plate, and also of explaining the extraordinary morphological changes which have led 

 to the terminal extremity of the alimentary canal of the starfish coming to occupy 

 the position of the stem in the Crinoid, an independent structure with which, in that 

 type, it always has been and still remains, unconnected, and from which it is alto- 

 gether distinct. 



MM. Danielssen and Koren 1 have ascribed, but in more guarded terms, a similar 

 homology to the dorsal appendage of Hyaster. They accept Perrier's deductions with 

 reference to Caulaster, but they do not discuss the question at issue, neither do they throw 

 any light upon the validity of the argument. They appear, however, to consider that the 



1 Nyt Mag. /. Naturvidensk., 1883, Bd. xxviii. 1, pp. 7-10; Den Norske Nordhavs-Expedition, xi., 

 Zoologi, Asteroidea, Christiania, 1884, pp. 102, 103. 



