1869.] BILLINGS — STRUCTURE OF CRINOIDS, ETC. 283 



that work. The following are the only authors, so far as I have 

 ascertained, who have given their opinions on this vexed question 

 during the last eleven years: — 



Prof. Wyville Thompson, op. cit., p. Ill (1861), agrees with 

 me that the lateral aperture is not an ovarian orifice, but, as we 

 have seen, is strongly opposed to the view that it is the mouth. 

 He calls it the anus. 



Prof. Dana (Man. Geol., p. 162, 1863) recognizes it as the 

 homologue of the simple aperture (oral and anal) in the summit 

 of those Crinoids which have but one. This is exactly my view. 

 [J. W. Salter agrees with Prof. Thompson, that it is the anus, 

 not the ovarian aperture. (Mem. Geol. Sur. G. B., vol. iii., 

 p. 286, 1866.) Prof. S. Lov(^n, of Stockholm, has described, 

 in the " Proceedings of the Royal Swedish Academy," 1867, the 

 remarkable sea Urchin, Leskia mirabilis (Gray), which has the 

 mouth constructed oh the same plan as that of the Cystidea, that 

 is to say, with five triangular valve-like plates, which are imme- 

 attached to the interambulacral plates, without the inter- 

 vention of a buccal membrane. After comparing this struc- 

 ture with the valvular orifice of Sphceronites pomum (Gyli.) he 

 says, " that the ' pyramid,' which in Leskia is the armature and 

 covering of the mouth, is the same thing in the Cystidea is now 

 quite certain ; in the last-named group it was, doubtless, also the 

 vent. The mouth does not lie where J. Miiller and Volborth 

 sought for it, viz. : in the centre of the ambulacral furrows ; and 

 the organ, interpreted as the vent by Volborth and von Buch, is 

 more correctly regarded as an external sexual organ." Geol. 

 Mag., vol. v., p. 181, Dr. Liitken's trans.] 



2. Oil the pectinated rhombs and calycine pores of the Cystidea. 



None of the organs of the Echinodermata have been the subject 

 of so much speculation as the calycine pores and the so-called 

 " pectinated rhombs " of the Cystidea. Their relations and 

 function long remained in doubt, but there seems to be now 

 sufiicient data to shew that they are respiratory organs, and also, 

 that they are the homologues of the tubular apparatus which 

 underlies the ambulacra of the Blastoidea. J. Miiller suo-gested 

 a comparison between these peculiar organs and the respiratory 

 pores of the Asteridce. (Uber den bau der Echinodermen, p. 63, 

 1854.) Prof. Huxley has placed them in the same relation. 



