TO THE EMBRYOLOGY OF AMPHIBIA. 49 



5). As to the first formation and growth of the archenterio 

 cavity, I agree mostly with Assheton ('94« p. 225-226, p. 227, p. 

 229). As represented in Fig. 63, the first trace of the blastopore 

 appears as a horizontal linear slit below the cell mass of the 

 equatorial zone, and is bounded by a kind of cells which is not 

 the true zonal but transitional between the yolk-cells and the zonal. 

 With Assheton we may consider this as formed by a splitting 

 between cells, or as a linear accummulation of the intercellular 

 space ; but we ought to remember that it is produced in direct 

 continuation of the inira-vitelline space, and must be regarded 

 morphologically as a modified form of invagination, the only 

 difference from the typical form being that cells situated on the 

 outer surface of the egg do not actually migrate inward. 



The further growth of the archenteron seems to take place very 

 much as Assheton describes : — posteriorly the cavity elongates by 

 the downward growth of the dorsal blastopore lip, in the manner 

 already described, while anteriorly it grows upward by a splitting 

 between cells or by an accummulation of intercellular space 

 accompanied by the multiplication and differentiation of cells 

 in situ. This splitting process for the formation of the archen- 

 teron cavity and the growth of the blastopore lips seems to me 

 also to be the direct continuation of the segmentation process. 

 For my part, however, I do not quite see the necessity for 

 distinguishing primary and secondary centres of growth, as 

 Assheton has done. 



The enlarging of the archenteric cavity as well as the reduc- 

 tion of the segmentation-cavity may be regarded from another 

 point of view, simply as a process of rearrangement of the yolk 

 cells in the egg interior. This has already been expressed by 

 Kopsch ('00) when he says " Da unsere Urteil hinsichtlich der 



