370 Wilson: [Vol. vi. 



sky finds, on the other hand, that the mesoblast-bands are from 

 the first perpendicular to the prototroch, — i.e. at right angles 

 to the position described by Gotte. 



My own results, briefly set forth in the paper referred to, 

 differ totally from those of Gotte and agree essentially with the 

 facts described by Salensky, though a study of the early stages 

 leads to a very different interpretation, (i) I showed that the 

 mesoblast arises from a single cell, the "second proteloblast " 

 (by no means, however, the cell described by Gotte), the off- 

 spring of which give rise to a V-shaped mass of cells, the two 

 arms of which form the mesoblast-bands. These bands have in 

 every respect the same position and relations as described by 

 Salensky. The apex of the V extends to the surface at the 

 posterior lip of the blastopore, so that the mesoblast-bands ap- 

 parently take origin in the ectoblast, as Salensky states. The 

 primary mesoblast-cell itself arises in a characteristic manner 

 from the large, left posterior macromere, precisely as in Clep- 

 sine, Rhyndiehnis, and in the gasteropod Crepidula, recently de- 

 scribed by Conklin (No. 4).^ (2) At the fourth cleavage a large 

 cell, the " first proteloblast," separates from that macromere 

 which afterwards gives rise to the mesoblast. From this cell 

 (which is evidently identical with the primary mesoblast of 

 Gotte) arises the entire ventral plate of the trochophore, — i.e. 

 the ventral neural plates, the seta-sacs, and probably a portion 

 of the nephridia. 



These results were published in a condensed form, in connec- 

 tion with the discussion of other questions, as I was still engaged 

 in the investigation of other features of the ontogeny. The paper 

 of V. Wistinghausen appeared soon afterwards, and his results 

 were independently attained, although my paper had been 

 received before their publication.^ The species investigated 

 was the " Nereis-form " of N. Dumerilii (the same as Gotte's 

 species), which lays its eggs in tubes and has a suppressed 

 trochophore, whereas Gotte's studies were based upon the 

 " Heteronereis-form,*' which has pelagic eggs and a free-swim- 

 ming trochophore. The results confirm my own on every essen- 



1 Through the kindness of Professor Conklin, I have been enabled to examine 

 many of his drawings and preparations in advance of the publication of the full paper. 



2 It may be added that the investigations described in the present paper were 

 practically finished before the appearance of v. Wistinghausen's paper. 



