678 
J. P. Munson 
of the culture medium, the metaplasm, from which the living substance 
grows. 
The yolk nucleus is not an amorphous, dead substance of little or no 
significance as has been assumed. It is the germ, so to speak, of the living 
part of the cytoplasm; and as it represents a centrosome and a sphere 
on a large scale, it gives an insight into that body, which the study of the 
little dot, usually called the centrosome, could never give. 
From what can be seen of the structure and history of the yolk nucleus 
in the egg of spiders, one would not hesitate to predict that this body, 
wlien introduced with the nucleus in fertilization, might regenerate the 
cytoplasm of the sperm, just as the ehromosomes form a male pronucleus. 
The discrepancy between the amount of cytoplasm in the egg und the 
sperm would thus really be of no consequence, as far as the hereditary 
qualities are concerned. Judged by appearances in the yolk nucleus, 
the centrosome is the cytoplasm packed into a very small area, the con- 
venience of which is evident in the sperm cell. 
The distribution of the amorphous granules in the yolk nucleus 
varies, being sometimes massed in the center, giving rise to the form 
represented in fig. 14. The granules obscure the delicate fibers in the 
center, which make np the essential part, the centrosphere. 
Yolk Nucleus (Vitelliue Body) in Egg of Limulus. 
In very young Limuli, fig. 25, when the ovarian tubes can first be 
seen, the oogonia form the lining cells of the tubes. Some of tliese beeome 
oocytes; which, as tliey grow, push out the basemcnt membraue, through 
openings between muscle fibers. In larger tubes when slit open and 
spread out flat, these openings appear as regulär oval areas surrounded 
by the muscle fibers, and connective tissue fibers. 
There is then visible, in properly preserved and stained material, 
at one pole of the nucleus of the oogonia, a body looking like arehoplasm. 
Sometimes it is spherical; sometimes it partly eneloses the nucleus as a 
crescent. In Lyons blue and saffranin, the crescent alone is deep blue, 
all other parts of the egg being red. As the oocyte begins to grow, and 
as it pushes out the wall of the tube, the blue body becomes more promi- 
inent, fig. 25. 
Superficial examinatiou gives one the impression that the blue body 
is a stieky, amorphous mass. But more carefid examination, with the 
highest magnifying powers, and with proper adjustment as regards illumiua- 
tion, reveals a central vesicle with a little dot in it, the centrosome. 
