ORAL AND APICAL SYSTEMS OF THE ECHINODERMS. 369 



In the young of both Echini (fig. ii) and Asterids (tig. 

 vii) there are two rows of plates surrounding the central 

 disc of the Apical system as in the Crinoids (figs, i, v). 

 It does not appear^ however, that the proximal ring of plates, 

 viz., the basals, is always developed in the Ophiurids. 

 Agassiz figures them in Ophiopholis hellis, but it is not easy 

 to determine their presence in any of Miiller's figures of 

 Ophiurid larvae, and in Metschnikoff's figure of the young 

 Amphiura there is absolutely no trace of them, though the 

 central disc and the radial plates are quite distinct. This 

 gives us a transitional stage from the other Echinoderms to 

 the Holothurians, in which not even a rudiment of an apical 

 system seems ever to make its appearance, though the oral 

 system may occasionally be very well developed {Psoitis). 



Besides pointing out the correspondence between the plates 

 at the apices of Urchins and Starfishes respectively, Prof. 

 Agassiz also instituted a comparison between these plates 

 and those forming the calyx of the Crinoids, which has 

 been extended by A. Agassiz in his memoir on the develop- 

 ment of the Starfishes. He says,^ " Were there a stem on the 

 central plate of its abactinal area, the young Starfish when 

 seen from the abactinal side would have all the appearance 

 of a Crinoid. The central plate corresponds to the basal 

 plate, the set of five plates in the angles of the arms to the 

 interradial plates, and the arm plates themselves to the 

 jadial plates of a Crinoid." And again : 



" I cannot agree with Professor Allman in considering 

 the central plate otherwise than as a solidified homologue 

 of the basalia of the other Crinoids figured by him ; the 

 only difference being that in some cases the plates com- 

 posing this piece are soldered together as in Comatula, while 

 in others they are kept distinct as in Coccocrinus and the 

 like." 



It will be seen from this last quotation that in Agassiz' 

 opinion the centrodorsal piece, or, as he calls it, the '^ cen- 

 tral plate ^^ of Comakda consists of five anchylosed basals, 

 and represents the central plate of the Apical system, i. e. 

 the subanal plate of the Echini. This opinion involves the 

 anomaly of the basis bearing cirrhi, which has been referred 

 to above in connection with Loven's views. Agassiz ignores 

 Dr. Carpenter's^ proof that the five interradial abactinal 



^ Loc. cit., pp. 62, 63. 



^ It should be mentioned here that Dr. Carpenter's memoir did not 

 appear until after the publication of the first edition of the ' Embryology of 

 the Starfish.' Agassiz, however, has taken no notice of it in the second 

 edition, except by referring to the figures of young Comatulae there repre- 



