200 p. HERBERT CARPENTER. 



den machte ; inclem also Fortsetzungen der ersten Tentakel- 

 gefasse in den aboralen Korpertheil hineinwachsen, bezeich- 

 nen die von ihnen gebildeten Ambulacralfelder nicht die 

 einzigen Strablsegmente, sondern wechseln regelmassig mit 

 den Interambulacralfeldern ab, welche gewissennassen ein 

 Strahlsystem fiir sich bilden, da auch ihre ersten Skelet- 

 anlagen gleichzeitig mit den ambulacralen aber unabhangig 

 von denselben und nicht paarig gerade so wie die radiaren 

 Riickenplatten der Seesterne entstehen." 



I must confess that I cannot agree with these conclusions 

 of Gotte's. On his own showing, the water-vascular stems 

 in the embryo Urchin do not alternate with the primary 

 tentacular cseca as in the Holothurians, and yet the anti- 

 mera they indicate are supposed by him to be homologous 

 in the two cases. If the relative positions of the primary 

 tentacular cseca and of the water-vascular stems are mor- 

 phologically as important as Gotte supposes, surely he is 

 somewhat inconsistent in completely disregarding them, as 

 in the case just quoted. Krohn^ states that the five 

 primary tentacles of the young Urchin disappear, instead 

 of persisting and branching as in the Holothurians ; but 

 according to Agassiz^ and Loven^ the mode of growth of the 

 new tentacles is the same as in the Starfishes. They are 

 formed in successive pairs at the bases of the large 

 primary tentacles, which are thus carried away from the 

 water vascular ring as the test enlarges and the radial stems 

 elongate. Agassiz* states positively that they pierce the 

 ocular plates, but Perrier^ altogether denies this. Whether 

 they are present in the adult or not, the fact that they ter- 

 minate the growing water-vascular trunks^ as in the Star- 

 fishes, is a sufficient argument against Gotte^s views, which 

 are based upon the hypothesis that the arms of the Starfishes 

 are not homologous with the ambulacral areas of the Urchins 

 and Holothurians, but with the buccal tentacles of the latter. 

 Upon this hypothesis the ambulacra of the Urchins are 

 supposed to be developed altogether from the right antimer, 

 like the apex of the Starfishes and the basis of the Crinoids. 

 Gotte therefore regards the aboral portions of the Starfish 

 body as equivalent, not merely to the apex, but to tne whole 

 convex portion of the Echinid shell, the ventral side of which 



1 Miiller's 'Archiv,' 1851, p. 351. 



2 'Revision/ p. 725. 



3 ' Loc. cit., p. 28. 



" ' Revision,' p. 682. 



' "Recherches sur I'Appareil Circulatoire des Oursins," ' Archives de 

 Zoologie Experimentale et Geuerale,' vol. iv, p. 623. 



