708 
J. P. Munson 
solution, it acts as a ferment or digestive fluid, causing Chemical changes 
resulting in metaplasm. 
6. The metaplasm when formed or in the process of forming may 
surround the nucleus giving rise to a deeply staining ring. More commonly 
it is formed around the centrosphere (see plates) wliere it often obscures 
the latter making an unusually large and often irregulär body. 
The metaplasm may form either within the sphere or at its periphery.. 
It then beeomes distributed in patches tliroughout the cytoplasm 
or as larger dark masses. It seems to flow with the currents of the cyto- 
lymph. 
Instead of these masses giving rise to a sphere, they are gradually 
absorbed as food by the sphere. 
7. The sphere is the organized part of the yolk nucleus, and it is an 
organic part of the living substance of the egg. It is the living frame- 
work of the body originally described as the yolk nucleus in spiders. 
8. The true yolk nucleus (vitelline body) is a centrosphere, not a mere 
accidental aggregation of granules, nor an artefact due to reagents. 
Many things in the cytoplasm of eggs designated by writers as yolk 
nuclei is not the true yolk nucleus (vitelline body) at all. Yery often 
they are mere metaplasm, deutoplasm or yolk masses that may appear 
in the neighborhood of the centrosome, but not necessarily, for that 
reason, produced by the yolk nucleus or centrosome. 
9. Typicallv, the yolk nucleus (vitelline body) is an aster with a centro- 
some and concentric circle as in dividing cells or in leucoeytes. 
10. The growth of the cytoplasm of eggs is largelv due to actual growth 
of this body. But partly also a mechanical expansion due to the accumula- 
tion of yolk. Growth seems to be by intussusception of metaplasm result- 
ing in the formation of true yolk bodies usually laid down in zones around 
the sphere, which in some eggs beeomes conspicuous as the latebra or 
nucleus of P ander. 
11. Metaplasm is absorbed by this body, and hence the cytoplasm 
grows from this point as a center. 
12. The relation of this body (vitelline body or yolk nucleus) to the 
germinal vesicle is such as exists between the centrosome and chromo- 
somes after karyokinesis. 
13. Its connection with the germinal vesicle and its peculiar structure 
is such that it serves as a reservoir into which the karyolymph is poured, 
and consequently beeomes the seat of assimilation and growth. 
14. The yolk nucleus (vitelline body) is often found to be an expanded 
aster, with radial fibers extending to the peripherv nearly, and concentric 
