676 
J. P. Munson 
The Yolk Nueleus of Spider’s Egg. 
In the very young eggs of spiders, the yolk nueleus has the structure 
and general appearance of the centrosphere of leucocytes and the fertüized 
egg of Ascaris, pl. XXXIV, figs. 68, 71, 74. It consists of a central granule, 
the centrosome, surrounded by a circle of microsomes, this being again 
surrounded by another zone of granulös, definitely limited by a ekele 
of large microsomes; and outside this, again, two more such circles. 
Most of the cytoplasm at this stage is such a centrosphere, the astral 
rays of which become lost in the general cytoreticulum of the thin outer 
layer of cytoplasm, pl. XXX, fig. 11. 
With the growth of the egg, the centrosphere assumes a variety 
of appearances as regards structural details. Owing to variable distribu- 
tion of granules, and the vacuoles formed from extruded karyolymph, 
the concentric circles become compressed, roughly illustrated by a folded 
Chinese lantern, giving rise to the concentrically striated appearance 
so marked in the yolk nueleus of these eggs, figs. 12, 13. 
It often remains closely applied to the germinal vesicle, figs. 12, 17, 
But as the egg grows, it may become separated from it, fig. 23. In such 
cases, however, it is sometimes possible to see radial bundeis of fibers, 
doubtless aggregated astral rays, connecting the two, figs. 15, 16, 23. 
On a superficial examination, the yolk nueleus looks like a spherical 
mass of archoplasm; but more careful study of favorablc preparations 
reveals a structure, which, in most respects, points to the original type 
of centrosome, with a central vesicle, containing a deeply staining dot, 
the centrosome, fig. 24. This is surrounded by zones, difficult to represent 
in drawings and equally difficult to describe. Sometimes the zones seern 
granulär ; sometimes they seem fibrous, varying somewhat with the magni- 
fying power used, figs. 19 and 20. 
As these bodies are so large that their diameter exceeds the thick- 
ness of a single seetion, the appearance varies, of course in different planes 
in which the body is cut. But the structure seems to be much the same 
in all radii. In my drawings, I have represented the seetion showing the 
central vesicle. Donbtless different hardening reagents produce differences 
in condensation. I have, therefore, made all my drawings of this egg 
from the same kind of material. 
The fibers of which this body is composed, are evidently continuous 
with the cytoreticulum of the general cytoplasm. Between the fibers 
are vacuoles or cavities, evidently corresponding to the meshes of the 
general cytoplasm, fig. 23. 
