17 



about the mid-region are 6 mm X 3 mm X 4 mm, the lower surface 

 of the vesicle where the wall is very thin having collapsed giving an 

 ovoid outline (Fig. 2 a). 



These figures indicate considerable individual variation. This is 

 further shown by a difference in the dimensions of the umbilical 

 vesicles of the 9 mm embryos given as 6 mm X 4,5 mm and 5,2 mm 

 X 3,7 mm respectively, as well as between these two and that of my 



Fig. 2 b. Region {B) of figure 2 a more highly magnified, showing a branchings 

 tnbule and character of the entodermal cells; also a small blood island in the angle 

 made by the two blood vessels above. X 320. Reduced ^/g in reproduction. 



own specimen of 9,2 mm (5 mm X 3 mm); and also that of a 9 mm 

 embryo described by Branca (4 mm X 2 mm). 



Again, in the matter of the presence of tubules, the same individual 

 variation obtains. In both of my own specimens the number of tubules 

 is large, though slightly less in the older sac. Meyer reports for 

 one of the 9 mm embryos many tubules and for the other some, while 

 that of the 14 mm embryo is said to have many. 



Auat. Adz. XXXVII. Aufsätze. 



