74 



K. MITSUKURI ; 



longitudinal section through the line A- 1' (Woodcut X, ^1) is given 

 in Woodcut XI, E. Actual sections have been figured several times 

 in Coniriimtions /, 7/7, anil IW I have never seeii a groove behind the 

 yolk-plug, between it and the epiblast, but I Ijelieve that this is due to 

 the rndimentary condition of the parts just here and that, theoretical- 

 ly, the section should 1)e as in Woodcut XI, F. Thus, the peristoinal 



Woodcut XI. 



Mcso 



'II I 1 1 1 n\ny\ '\ 



zzinimzr 



E 



Yk. Plug 



Yk PJuff, 



-Hyp. 



mesoblast is jjroliferated partly from the cell-mass in ([uestion and 

 partly from the epiblast, in the shape of an open fan from all around 

 the yolk-plug except the anterior edge. At the edge of the a,nteri(^r 

 transverse part of the blastopijre, the peristomal mesoblast is continued 

 into the gastral mesoblast, for the details of whose origin the reader is 

 referred to Guuirlbutions I, and J 11. 



When the medullary folds arise and reach the posterior part of 



