APPENDIX. 



NOTE A. 



(Pages 2, 157, and 168.) 



On the Homologies of the Cpjnoidal Calyx m the other Echinoderms. 



The relations of the plates which enter into the composition of the calyx of a Crinoid 

 to those constituting the apical system of an Urchin or a Starfish are still the subject of 

 much discussion. 



The apical system of an Urchin, as described by Loven,^ consists typically of a dorso- 

 central plate enclosed ■svdthin two rings of five plates each. The plates of the proximal 

 ring (genitals, Auct.) are interradial in position, while those of the outer ring (oculars) are 

 radially situated. Believing that the dorsocentral is represented in the Pentacrinoid 

 larva of a Comatula by the terminal plate at the base of the stem,"^ I have suggested that 

 the basals of the Pentacrinoid are homologous with the so called genitals of an Urchin ; 

 while the ocular plates of the latter correspond to the radials of the Crinoid. So far as the 

 basals and radials are concerned this view is fundamentally the same as that previously 

 expressed by Loven and Agassiz, allowance being made for the difference between their 

 terminology and that employed by myself; so that the homology between the basals and 

 radials of a Crinoid and the two rows of plates surrounding the dorsocentral of an 

 Urchin has been pretty generally accepted. 



Dr. R. Hoerues,^ however, objects to this homology (which he associates with my 

 name) on the ground that the resemblance should be most marked in the geologically 

 oldest tj^ies, " was keineswegs der Fall ist, da gerade der ScheitelapjDarat der Pala3chinoiden 

 durchaus nicht an die Basis-Entwickelung der Crinoiden-Kelches sich anschliesst." 

 This objection may be answered in two ways. 1. Loven* says that the general formula 

 of the apical system of Echinoidea " has remained, more or less altered, but always recognis- 

 able, from Palaeozoic to recent time." 2. The positive fact that the basals and radials of 



1 Etudes sur les Ecliinoiclees, K. Sve7isk. Vetensh. Akad. Handl., Bd. xi., 1874, No. 7, p. 65. 



2 Quart. Joum. Micr. Set., 1878, vol. xviii., N. S., p. 374. 



3 Elemente der Palteontologie (Palceozoologie), Leipzig, 1884, p. 130. 



* On Pourtalesia, a genus of Echinoidea, K. Svendc. Vetcnsk. Akad. Handl., Bd. xix., 1883, No. 7, p. (i2. 

 (ZOOL. CH.\LL. ESP. — PART SXSII. — 1884.) li 50 



