54 



MEMOIRS OF THE NEW YORK ACADEMY OF SCIENCES 



was the solid rudiment of the neurenteric canal. The radial arrangement in this 

 problematic cell-mass at an earlier stage (figure 10, A) suggested to him an in vagi- 

 nation, and he considers this to be the equivalent of the " prostoma " of KUPFFER, 

 differing from it only in that the latter opened directly to the surface instead of 

 being covered by the superficial layer. Kupffer's Vesicle represents, according to 



FIGURE 10. 



A. Sagittal section through posterior border of 

 blastoderm of Carassius (after Kowalewski) show- 

 ing supposed invagination occurring at this point. 



B. Section showing Kupffer's Vesicle in Caras- 

 sius (after Kowalewski). 



FIGURE 11. 



KOWALEWSKI, a small but important part of the " Gastruladarm," the rest of which 

 is represented by the uncovered part of the yolk. 



It is surprising, in view of this brief and accurate description presented as long 

 ago as 1886, that the prostomal thickening has been all but ignored by subsequent 

 investigators. Both HENNEGUY ('88) and VIRCHOW ('95) have seen cells in this po- 

 sition, but do not regard them as being of constant occurrence nor of any theoret- 

 ical importance. (Concerning BERENT, see below.) 



Conclusive Evidence of the Preceding View. The 

 present writer first noticed the prostomal mass of cells in 

 the blastoderm of Amiurus (figure 11), regarding it at the 

 time as a mere thickening of the superficial layer. Upon 

 following out the subsequent course of development and 

 comparing with the condition in other forms, I was led to 

 a view of its significance quite similar to that expressed in 

 KOWALEWSKI'S later paper, even before I had seen the lat- 

 ter. The presence of the nick or indentation often found 

 in this cell-mass, and the grouping of its cells (figures 5 and 10, A) have been noted 

 by KOWALEWSKI and offered by him as an evidence of invagination. Another ap- 

 pearance, which I noticed in an embryo of Amiurus at the time of the formation of 

 Kupffer's Vesicle (figure 12) pointed to an obvious relation between this vesicle and 

 the supposed invagination. In a paper before the New York Academy of Sciences 

 ('99, b) I advocated a view similar to that of KOWALEWSKI. As then stated, my 

 opinion was somewhat different from that presented in the present paper. 



The chain of evidence was not complete, however, until a form had been found 



Pr 



Section showing thickening of 

 superficial layer (Pr) on pos- 

 terior margin of early Amiurus 

 blastoderm. 



