A Comparative Study of the Structure and Origin of tlie Yolk Nucleus. 681 
reside in the nucleus alone, but in the nucleus and cytoplasm combined. 
The yolk nucleus, as here described, being fundamentally an attraction 
sphere, consisting of a central body, circles of granulös and astral rays, 
represents that part of the cytoplasm by which that persistence can be 
accounted for. 
As in many other cggs, so in this, a ring around the germinal vesicle 
sometimes appears. I have seen this very clearly also in the living egg. 
Such a ring is represented in fig. 38. It is clearer or lightor than the onter 
zone of cytoplasm, and it is bounded by a thin layer of fibers, which seem 
to proceed at onc pole of the germinal vesicle, from an obscurc sphere, 
around which there are indistinct evidences of astral rays. 
In this casc the germinal vesicle is normal, having chromatin arranged 
in the usual way in these eggs, viz., as a nuclear reticulum with a large, 
distinct nucleolus in which there is a vacuole. 
But cases are frequently met with in which the inner zone is particu- 
larly dark and granulär, especially when stained with hematoxylin; but 
distinct also, when stained with picrocarminc or a variety of other stains, 
fig. 43. 
In many cases, as here, the ring is broadest at one pole; and often 
forms an irregulär mass of closelv packed granulös, or eise, more or less 
scattered irregularly throughout the central part of the cytoplasm. 
Always in these cases, so far as rny observations on this egg go, the 
germinal vesicle is large and spherical, showing no evidence of slirinkage. 
But it seems to be entirely devoid of chromatin, there being no nucleolus 
and only very slight traces, if any, of the stainable substance correspond- 
ing to the nuclear reticulum of the more usual forms, such as is shown in 
figs. 38, 46. 
I have been inclined to consider this a pathological condition of the 
egg. It is not an artefact, as it occurs in the best preserved material, and 
the entire egg shows no evidence of slirinkage of any kind, that might be 
attributed to bad preservation. 
If the eggs showing these features, fig. 43, are normal, and if the 
inner granulär zone is due to extruded chromatin, it is certainly difficult 
to have much faifh in the individuality of the chromosomes. The contents 
of the distended nucleus looks like a colorless precipitate, such as one 
might expect from the action of acids on Solutions. 
Aside from the absence of chromatin, of which I have no explanation 
to offer, the granulär ring may possibly be accounted for as was the meta- 
plasm in the egg of the tortoise; namely, a combination of karyolymph 
from the germinal vesicle with unassimilated food in the cytoplasm derived 
