119 
ova of the eleventh day it measured 223 mm in diameter, and in the 
smaller ova of the twelvth day 197 mm in diameter, that is in both 
cases about one fifth of the whole diameter of the vesicle. 
In the germinal area the nuclei were larger and more closely 
packed but cell outlines were not distinguishable. When it was viewed 
from the exterior and the polygonal cells were traced towards it they 
seemed to gradually disappear at its periphery and they certainly 
could not be traced over it. 
When viewed from the interior the germinal area seemed to pro- 
ject into the interior of the vesicle and the polygonal cells could be 
traced over its surface though with some difficulty for their outlines 
were not easily definable. 
| H 
£ ee, 
eo 
Fig. 1. Camera drawing of a section through a portion of the distal pole of a 
ferret’s ovum at the eleventh day, 420. 
Fig. 2. Camera drawing of a section through the germinal area of{ a ferret’s 
ovum at the eleventh day, 420. 
A Zona pellucida, EZ Epiblast.  Hypoblast. 
The examination of sections each of which was 5 w thick dis- 
closed the true nature of the vesicle Fig. 1 and Fig. 2. The most 
external cowering was an uniformly thin zona pellucida. A immedia- 
tely within this lay the cellular wall for no vitelline membrane was 
discernable. 
In the germinal area there were two layers between the zona 
pellucida and the cavity of the vesicle. The external layer E (Fig. 2) 
consisted of granular protoplasm containing many comparatively large 
