Cuap. I. DEVELOPMENT OF THE YOLK CELLS. 463 
ules; whilst the germinal vesicle exhibits considerable elasticity when pressure is 
removed, and will not burst till the last moment, if we may so express it, and 
then very suddenly, as if it had sustained great tension in some kind or other of 
restraining envelope. 
There remains but one question to answer respecting the granular period in 
the growth of the yolk, before we arrive at the turning point, which reveals to 
us an entirely new and important feature in the life of the egg 
mation of genuine yolk cells. 
sy of an inch in diameter? 
How constant are the denser rings (PI. 8, fig. 
of granular matter, already mentioned above, which may be seen in eggs of 
It is not yet possible to answer definitely this 
namely, the for- 
18a) 
about 
oo? 
ques- 
tion; but this much is certain, that. such phases are so frequently met with as 
to warrant the conclusion that they are to be considered as the prevailing state 
of the egg at this age. 
darkly outlined (PI. 
lighter circles exhibit only the faintest traces of minute, dot-like particles. 
The granules of the rings are rather coarse, but not 
8, fig. 18b) nor irregularly shaped as heretofore, and the 
In eggs 
considerably larger than this, (Pl. 8, fig. 19b,) we may meet with two rings of 
similar structure, (fig. 19,) separated by corresponding clear spaces. 
SECTION 
Per 
DEVELOPMENT OF THE YOLK CELLS. 
Formation of the Ectoblast. 
1 Thus far we have employed, in our descriptions 
of the egg and its contents, the nomenclature gener- 
ally in use to designate its different parts, and those 
of the cell. But this nomenclature, framed to ex- 
press particular views respecting the mode of forma- 
tion and the functions, of these parts, is completely 
theoretical in its meaning. It appears desirable, there- 
fore, now that we are about to consider more fully 
the origin and successive growth of the yolk cells, 
to discard eyery technical expression which may 
imply a theory, and to adopt such only as designate 
the natural relations of the objects under considera- 
tion, especially since the views to which we have 
arrived cannot be reconciled with the theories which 
Thus far we have considered the yolk as a whole. 
We now proceed to describe its cellular development.’ 
The first change noticeable 
the current nomenclature is intended to express. 
For instance, in the case of a nucleolated cell, the outer 
envelope is described as formed around a nucleus, 
in which latter the nucleolus is developed. The 
outer cell membrane would thus inclose, at a later 
time, a mass accumulated around a nucleus already 
formed, as its name implies, and the nucleolus would 
be developed within the nucleus. For similar rea- 
sons we shall, hereafter, also avoid the expressions 
“parent and daughter cells.” But, whatever be the 
mode of origin of cells and of their parts, there is, 
in a perfect cell, an outer envelope, containing an- 
other vesicle, in which is seen another smaller body 
These parts are therefore designated in the sequel 
