REPORT ON THE ASTEROIDEA. 131 
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 “ pédoncule 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 “pédoncule 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 ‘ pédoncule 
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’ have ascribed, but in more guarded terms, a similar 
homology to the dorsal appendage of Jlyaster. 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. f. Naturvidensk., 1883, Bd. xxviii, 1, pp. 7-10; Den Norske Nordhays-Expedition, xi., 
Zoologi, Asteroidea, Christiania, 1884, pp. 102, 103. 
