TN THE MOEPHOLOGtT OF THE CYSTIBEA. 37 



perhaps, in LesTcia mirahilis. But so far as the other groups are 

 concerned there can now be little doubt that the presence of five 

 primary plates developed interradiallj on the left larval antimer 

 is a fundamental morphological character. Bury * has recently 

 shown that the terminal plates of the Stellerid arms are the radial 

 plates of the left antimer, corresponding to the radials of the ab- 

 actinal system. They may, or may not, be present in other 

 groups, a point which I hope to discuss at some future time. But 

 I am most strongly of opinion that the plates forming the apical 

 and oral systems of Echinoderms cannot be left out of consider- 

 ation in any discussion respecting the phylogeny of the group ; 

 and if Semont would modify hisTentactula theory to the extent 

 of admitting that his ancestral larval form (Penfactced) had both 

 abactinal and actinal radial and interradial plates, I should be 

 greatly inclined to accept his general conclusions. He assumes, 

 however, that the ancestral Echinoderm had " kein festes Skelett," 

 and on p. 108 states his opinion that no true homologies are 

 traceable in the apical system, " sondern nur sehr tauschende 

 Analogieen." His acquaintance with the literature of the sub- 

 ject does not seem to be very extensive, for he states in a later 

 paper | how " zwei eifrige Anhiinger Carpenter's wie Sladen 

 und Bury die Terminalia der Asteroiden und Ocellarplatten der 

 Echinideu fiir nicht homolog den ersteu E-adialia der Crinoideen 

 halten." Semon appears to be altogether unaware tbat as long 

 ago as 1884 I accepted Sladen' s suggestion that the homologues 

 of the radials of a Crinoid are to be found, not in the terminals 

 of Asterids, but in the radial plates of the apical system §. If 

 Semon will refer to tbe two papers of that date by Sladen and 

 myself II, or to the chapter on this subject in the " Report on the 



* Quart. Journ. Micr. Sci. 1889, vol. xxix. pp. 432-442. 



t " Die Entwickelung dei- Si/ncqita cligitcda, uud die Stammesgeschichte der 

 Echinodermen," Jenaische Zeitscb. Naturwiss. 1888, xxii. Bd. N. F. sv. p. 78 (of 

 separate copy). 



I 'Die Homologien iunerhalb des Eehinodermeustammes," Morphol. Jahrb. 

 1889, Bd. XV. p. 299. 



§ On this subject Neuinayr remarked (p. 500) : — " Audi bei Zoroaster fulg ens 

 (Quart. Journ. Micr. Sci. vol. xxiv. Taf. 1. fig. 16) ist die von Sladen als 

 ' Eadiale ' bezeichnete Platte nur das grosste proximale Grlied der bomologen 

 Keibe dorsaler Armtafeln." It is curious tbat Neumayr sbould not have re- 

 membered that the same description applies to the radial plates of a Orinoid. 



II Quart. Journ. Micr. Sci. 1884, vol. xxiv. pp 3, 32. 



