MUSEUM OF COMPARATIVE ZOOLOGY. 137 



The orals originate near the margin of the pentagonal larva, and have a 

 part of their extent at least on the abactinal side. A single oral which 

 is pierced by an opening is larger than the rest, and is one of the first to 

 form. This is supposed to he the same as the madreporic plate. It is 

 larger than the remaining orals, and like them, by the increase of the 

 plates in the interradii between them and the dorsocentral, is forced in 

 the growth of the disk to the actinal side of the body. In their young- 

 est condition the orals resemble other plates in their spicule-like shape. 



The literature written by those who have observed the development of 

 the plates of Amphiura does not agree with Sladen when he says : * 

 "The orals and some of the accompanying plates of the actinal hemi- 

 some next appear [after radials and terminals] before any trace of the 

 dorsocentral plate is present." If he means that all the orals appear be- 

 fore the dorsocentral, it cannot have been knowledge derived from what 

 has been published on the development of Amphiura ; for Ludwig has 

 said nothing to support such a statement, nor does his figure show more 

 than one oral before the formation of the dorsocentral. On the other 

 hand, Krohn in 1851 and Metschnikoflf f eighteen years after figure a 

 well-developed dorsocentral plate before any sign of an oral. It will not 

 be claimed that the figures of the last-mentioned naturalists are perfectly 

 accurate in this particular, for it is believed that the madreporic plate 

 ought to have been represented by them in figures showing the imma- 

 ture dorsocentral, but one cannot suppose that they support Sladen's 

 statement. In Ludwig's Figs. 17, 23, in which no dorsocentral exists, 

 the madreporic plate is formed, but there is no other oral represented. In 

 his Fig. 19, where the dorsocentral is well developed, one of the orals is 

 little more than a three-pronged spicule. Evidently here the dorsocentral 

 has antedated in formation one of the orals. My preparations teach me 

 that the dorsocentral is of considerable size before some of the orals. J 



anatomischen Bemerkungen iiber die Echinodermen iiberhaupt, Zeit. f. Wiss. 

 ZooL, XXXIV. pp. 318-322. Neue Beitrage zur Anatomie der Ophiuren, Zeit. f. 

 Wiss. ZooL, XXXIV. p. 342. Entwickelungsgeschichte der Asterina gibbosa, Zeit. 

 f. Wiss. ZooL, XXXVII. Carpenter, Quart. Joumi. Micros. Sci. XX. {ns). 



* Op. ciL, p. 29. t Op. cU., PI. III. Fig. 17. 



X What is said above is on the supposition that Sladen calls the orals the plates 

 (5, PI. I. Fig. 13), and no others. I think I am just in this supposition. If however 

 he includes among orals the spoon-shaped plates and the adambulacral, as might 

 be done, my criticism above would be unjust, and I gladly withdraw it. 



Sladen's paper on the "Primary Larval Plates of Brachiate Echinodenns" devotes 

 some space to the homologies of the odontophore of the starfish. As he does not 

 consider in this discussion the first pair of adambulacral and the spoon-shaped plates 



