H. W. Acton and W. F. Harvey 
265 
oocyte in Antedon bifida, states that “ throughout the growth of the 
oocyte the nucleolus intermittently discharges groups of deeply staining 
basophile granules into the cytoplasm. In the young oocyte these 
nucleolar spherules remain unchanged and slowly accumulate in the 
cytoplasm where they form small groups near the germinal vesicle. In 
slightly older oocytes, the increased fluidity of the cytoplasm (which results 
from the progressive accumulation of the metaplastic material in 
preparation for yolk formation) causes the discharged nucleolar matter 
to lose its spherical form and to diffuse into the neighbouring cytoplasm. 
The deeply stained area of protoplasm to which this diffusion gives rise 
is the yolk nucleus. The yolk nucleus assumes the form of a concavo- 
convex lens and embraces the germinal vesicle. During yolk formation, 
2 
Fig. 2, 
Fig. 1 
Fig. 1. 1. Nucleolus. 2. Discharged nucleolar particles. 
Fig. 2. 1. Nucleolus discharging nucleolar granules. 2. The yolk nucleus. 
(From Chubb, reproduced in Adami’s General Pathology.) 
the yolk nucleus passes to the pei’iphery of the ovum, a migration also 
shared by the peripheral nucleolar spherules. The yolk nucleus is 
therefore a region of the cytoplasm into which waste, dischai-ged from 
the nucleolus has taken place.” (Text-figs. 1, 2.) Macallum (1891) in 
his study of the germinal vesicles of the developing ova of the Necturus, 
found at a certain stage of development, that the nucleoli occurred at 
the periphery of the germinal vesicle, in apposition with the vesicular 
membrane. The nucleoli vary in size but are somewhat spherical in 
shape. At this stage of development no yolk spherules are seen. By 
employing indigo-carmine as a stain he found that these peripheral 
nucleoli took on a blue stain whilst the nucleolus and cytoplasm were 
stained red. At a later stage, when yolk formation had occurred, the 
