X.] 



FORMATION OF THE LAYERS. 



317 



cells, a columnar epiblast and a layer of flattened hypo- 

 blast. 



Fm. 97. 



SECTION THROUGH THE NEARLY CIRCULAR EMBRYONIC AREA OF 



A RABBIT OVUM OF Six DAYS. 



(From Allen Thomson, after E. van Beneden.) 



ect. upper layer ; mes. middle layer ; ent. true hypoblast. 



FIG. 98. 



SECTION THROUGH THE BLASTODERM OF A RABBIT ON THE 

 SEVENTH DAY : TAKEN IN FRONT OF THE PRIMITIVE 

 STREAK. 



Half of the area is represented. 



Towards the end of the sixth day the embryonic 

 area of the rabbit, which has hitherto been round, be- 

 comes oval. 



A diagrammatic view of the whole blastodermic 

 vesicle at about the beginning of the seventh day is 

 given in Fig. 99. The embryonic area is represented in 

 white. The line ge in B shows the extension of the 

 hypoblast round the inside of the vesicle. The bias- 



