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



form which they have described so ably under the name of Ilyaster mirabilis supports 

 the views upheld by Perrier, and should be ranked in the same category as forming " a 

 connecting bnk between Crinoidea and Asteroidea" on account of the presence of its 

 remarkably developed dorsal appendage. 



It is probable that the apical plates of Ilyaster have never yet been observed (they 

 had not been seen when the type, which is probably tox> large to possess them, was 

 described) ; and I venture to consider that the abactinal prolongation in Ilyaster, like that 

 in Caalaster, is also an anal funnel (whether functional or not I cannot say), and that, 

 such being the case, it does not lend any support to the view that this remarkable 

 development is in any way homologous to the stem of a Crinoid. I would further remark 

 that this most interesting form Ilyaster mirabilis appears to me to be more nearly allied 

 to the Astropectinidaj than to any of the genera which I have included in the family 

 Porcellanasteridae. 



With reference to the foregoing remarks, it may be pointed out that Dr P. Herbert 

 Carpenter 1 hesitates to accept the homology of the dorsal appendage of Caulaster and 

 Ilyaster with the stem of a Crinoid, and considers that the assumption is not yet satis- 

 factorily proved. Carpenter also points out that Perrier 's comparison of the plates round 

 the dorsal appendage of Caulaster with those forming the periproct of an Urchin cannot 

 be followed out in detail, as, according to Perrier's description, the apical system of 

 Caulaster consists, not of genitals and oculars (basals and radials) as in an Urchin, but of 

 under-basals and basals. With these views I entirely concur. 



In conclusion I would add that I am altogether at a loss to reconcile Perrier's view 

 according to which "le dos des Asteries correspondrait a, la region buccale des Oursins et 

 non a leur region anale " 2 with his comparison of the apical system of Caulaster with that 

 of an Urchin. 3 For either the proposition is self-contradictory, or, if it be true that the 

 abactinal area of Caulaster corresponds to the apical region of the Echinoid, whilst the 

 abactinal area of all other Asterids corresponds to the buccal region, it seems to me only 

 another way of saying that the abactinal area of Caulaster corresponds not to the 

 abactinal area, but to the actinal area in other Asterids. I will not do M. Perrier the 

 injustice of thinking for a moment that he believes this to be the case. 



For my own part I consider, along with Loven, 4 Carpenter, 5 Agassiz, 6 and other 

 naturalists, that the buccal region of an Asterid, of an Echinoid, and of a Crinoid are cor- 

 respondent, and consequently that the apical systems of an Asterid or Echinoid and the 

 calyx of a Crinoid are homologous parts. 



1 Report on the Crinoidea, Voyage of H.M.S. Challenger, Zool. Chall. Exp., 1884, Part xxxii. p. 401. 



2 Nouv. Archives Mus. His. Nat., 2e S<5r., 1884, t. vi. p. 162. 



3 Comptes rendus"(T>ec. 1882), t. xcv. p. 1380. 



4 E*tudes sur les Eehino'idees, E. Svensk. Vetensk, Akad. Handl., 1874, Bd. xi. No. 7. 



5 Report on the Crinoidea, Voyage of H.M.S. Challenger, Zool. Chall. Exp., 1S84, Part xxxii. p. 401. 



6 Mem. Mus. Comp. Zool, Harvard, 1877, vol. v. No. 1. 



