the Crinoidea, Cystidea, and Blastoidea. 257 



moutli constructed on the same plan as that of the Cystidea — 

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

 immediately attached to the interambulacral plates, without 

 the intervention of a buccal membrane. After comparing this 

 structure with the valvular orifice of Sphceronites pomum 

 (Gyll.), he says : — " that the * pyramid,' wliich in Leshia 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 moutli docs 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 ex- 

 ternal sexual organ." (Grcol. Mag. vol. v. p. 181, Dr. Llitken's 

 transl.)] 



2. On 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 rela- 

 tions and function long remained in doubt; but there seems 

 to be now sufficient data to show 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 suggested a comparison between these peculiar or- 

 gans and the respiratory pores of the Asteridas (Ueber den 

 Ban der Echinodermen, p. 63, 1854). Prof Huxley has placed 

 them in the same relation (Medical Times, Dec. 185G). Eich- 

 wald calls them respiratory pores (Lethasa Rossica, vol. i. 

 p. G14: 1860). Prof. Dana says " they are probably connected 

 with an aquiferous system and respiration " (Man. Geol. 

 p.l62 : 1863). Mr. Rofe, after showing that their structure is 

 the same as that of the striated surfaces between the rays of 

 Codaster^ says, " From the construction of these striations on 

 the face of Cadaster^ and on the * pectinated rhombs ' of the 

 Cystidea, may we without assumption suggest the possibility 

 of their being respiratory sacs, lined with cilia, and constructed 

 of a porous test, through which air from the water could pass 

 by diiFusion" (Geol. Mag. vol. ii. 251 : 1865). As for myself, 

 when I prepared my Decade on the Cystidea, I gave this sub- 

 ject a great deal of consideration, and studied a large number 

 of specimens, but could arrive at no conclusion satisfactory to 

 myself. I am now convinced that the view of the above- 

 named distinguished authors is the correct one. These are 

 respiratory organs. In all the species in wliich they occur 

 they seem to be constructed on the same general plan, i. e. 



