THE EGG 29 
tened against the vitelline membrane, the inner surface re- 
maining convex (Fig. 8). The point on the surface to which 
the germinal vesicle migrates is situated away from the surface 
of the ovary, and thus in the position of the pedicle of the 
follicle, when the latter projects from the surface of the ovary 
(Sie Oe 
The formation of the yolk has not received the attention that 
the subject deserves; and it is possible to give only a very general 
outline. While the nucleus is still in the center of the egg a 
very dense deposit of extremely fine granules is formed around 
it, and gradually extends out towards the periphery of the cell, 
but does not involve the peripheral layer of protoplasm, which 
is shghtly thicker at the innermost side of the follicle correspond- 
ing to the stalk. When the ovum has reached a size of approx- 
imately 0.66 mm, the nucleus moves towards the thickening 
of the peripheral layer and enters it, lying very close to the vitel- 
line membrane. 
The very finely granular central aggregation of yolk-granules 
represents the primordium of the latebra or central mass of the 
white yolk. After the nucleus has reached the periphery, or 
while it is still on its way, the yellow yolk begins to be formed 
by the peripheral layer of protoplasm. Small yolk-granules 
arise near the inner margin of the peripheral layer of protoplasm 
and increase in size; each becomes enclosed in a vacuole which 
grows to a considerable size, so that the accumulation of vacu- 
oles on the inner surface of the peripheral protoplasm soon 
produces a kind of emulsion; this appears in section like a 
reticulum, the spaces of which are the sectioned vacuoles, and 
the strands the remains of the protoplasm in which the 
vacuoles are embedded (fig. 7). This layer lies between the 
peripheral unmodified protoplasm and the white yolk. <A sim- 
ilar process is going on at the same time in the central pri- 
mordium of the white yolk, but the vacuoles and the granules 
are smaller, and the contrast between the white and yellow yolk 
is obvious (Fig. 7). 
Successive layers of yellow yolk are deposited around the 
central mass of white yolk by the activity of the peripheral layer 
of protoplasm. Thus one can understand in general how the 
concentric arrangement of the yellow yolk is produced. But the 
alternation of layers as seen in a section of the hardened yolk 
