2/6 



BASHFORD DEAN. 



do not occur throughout a narrow zone but extend peripherally 

 over a wide area of the yolk. In connection with this remark- 



BP 





FIG. 10 A. Detail of archenteric region of preceding section. 



FlG. 10 B. Detail of antero-dorsal germinal wall of preceding section. Observe 

 the cells arising in the overhanging germinal wall below and between the points * * 



I'M UP 



FIG. II. Early gastrula. Sagittal section. A. Archenteron. BP. Region of 

 blastopore. PM. Posterior cell mass (= ventral lip of blastopore). SC. Segmenta- 

 tion cavity. Yolk nuclei are below the asterisks. The arrow denotes the general 

 axis of the archenteron. 



able vacuolization of the yolk mass the extension of the nucleus- 

 bearing zone is to be considered a process of actual fragmentation 



