IN THE MOHPHOLOGY OF THE CTSTIDEA. 35 



I have designedly abstained from all speculations respecticg 

 the origin of the Echinoderms, though I have once or twice 

 alluded to various facts wliich seem to show that the Crinoids are 

 in a more embryonic condition, and consequently represent an 

 earlier phylogenetic stage than the other classes. But this is a 

 very different thing from regarding them as the ancestral forms 

 of the Urchins, and I would ask the Messrs. Sarasin to quote any 

 passage from my writings which shows that I have ever held this 

 view. 



If I understand them rightly, they altogether deny that any 

 homology can be traced between the calyx-plates of a Crinoid and 

 those forming the primary apical system of an unstalked Echino- 

 derm *. They do not seem to consider the embryological evidence 

 (which has been greatly strengthened since their memoir appeared 

 by the researches of Eewkes t and Bury $) as deserving of any 

 consideration at all, for they say on p. 147, " Das Auftreten von 

 Kreisen aus je fiinf oder zehn platten bei Echiniden uud Crinoideu 

 beruhrt auf secondiirer Vereinigung urspriiuglich ungeordneter 

 kleinerer Plattchen, analog dem Verschmelzen von primaren 

 Ambulacralplatten zu Grossplatten ; " while on p. 151 they 

 become somewhat sarcastic about the variations in the arrange- 

 ment of the apical plates of Ophiurids, and the difficulty of 



* Stiirtz has recently made an extraordinary blunder respecting the apical 

 system of the Ophiurids (loc. cit. p. 241). Eeferring to Neumayr's remarks 

 upon it, he asserts that the centrodorsal rosette of these forms represents "das 

 Mundskelet in der dorsalen Ansicht," and he thinks that on this subject " dilrfte 

 jetzt wohl kein Zweifel mehr bestehen." Stiirtz is here confusing what Boehm 

 called " die fiinfteilige Rosette " in thinly-plated disks with the rosette cf 

 primary plates in the more heavily-plated forms. The former appearance is, no 

 doubt, due to shrinkage and to the prominence of the mouth-skeleton beneath ; 

 but if Stiirtz will look at the figures of the dorsocentral systems of Ophiomusium 

 and Ophioglypha in the early plates of Lyman's ' Challenger ' Report, he will 

 discover his mistake. The dictum that the very substantial rosette of such 

 forms or that of Ophwj^yrgus Wyville-thomsoni (pi. ix. figs. 16, 17) is a dorsal 

 view of the mouth-skeleton, can only be due to an inadequate knowledge of the 

 subject. His error is the more curious as he refers to the " Riickenappendix " 

 of Ojphio'pyrgus on p. 244.. 



t " On the Development of the Calcareous Plates of Amjihiura," EuU. Mas. 

 Oomp. Zool. 1887, vol. xiii. pp. 120-131 ; and " On the Development of the 

 Calcareous Plates of Asterias," ibid. 1888, vol. xvii. pp. 4-45. 



+ " The Early Stages in the Development of Antedon rosacea" Phil. Trans. 

 1888, B, pp. 269-293; and "Studies in the Embryology of the Echinoderms," 

 Quart. Journ. Micr. Sci. 1889, vol. xxix. pp. 432-445. 



a* 



