360 



THE RABBIT. 



single layer of flattened pavement cells, thickened in their 

 centres by the nuclei, but very thin at their margins. 



Beyond the embryonal area, the lower layer, or hypoblast, has 

 extended further round the vesicle than before, so that it now 

 lines about a third of the entire vesicle ; the wall of the remain- 

 ing two-thirds still consists of a single layer of flattened cells, 

 continuous with those forming Kauber's layer. 



The seventh day. During the seventh day, and often before 

 the close of the sixth, the blastodermic vesicle loses its spherical 



-PS 



PS 



PC 



FIG. 143. 



FIG. 143. The blastodermic vesicle of a Rabbit at the end of the seventh 



day, seen from above. (Modified from Kolliker.) x 12. 

 AD, embryonal urea. AG, will of blastodermic vesicle. M, dotted line indicating 

 the boundary of the niesoblast. PS, primitive streak. 



FIG. 144. -The embryonal area of a Rabbit at the middle of the eighth day. 

 (Modified from Kolliker.) x 12. 



N"F, neural fold. !N"G, neural groove. PG, primitive groove. PS, primitive 

 streak. 



shape, and becomes ellipsoidal (Fig. 143). The average dimen- 

 sions of the entire vesicle at the end of the seventh day are 

 from 4-5 to 5 mm. in length, by 3 '5 to 4 mm. in width; but 

 individual specimens may considerably exceed these limits. 



The embryonal area (Fig. 143, AD) is now distinctly pyriform 

 in outline, measuring on an average 1-5 mm. in length, by 

 1 mm. in width. Its longer diameter corresponds to the axis 

 of the blastodermic vesicle, and, as a rule, to that of the uterus 

 as well. From their relations to the embryo at a later stage, 



