43 8 
MONTGOMERY. 
[Vol. XV. 
that a dense condensation of the fine granules of which they 
are composed takes place. They continue to increase in size, 
and gradually stain deeper as they do so, until they attain about 
the dimensions given in Fig. 217 ; but I am unable to deter¬ 
mine whether they all reach exactly these dimensions before 
the metaphasic changes commence. At the conclusion of this 
period of their development they are large bodies, regularly 
spherical or oval in outline, and apparently without a limiting 
membrane ; especially characteristic is their homogeneity and 
their intense staining. 
Metaphasis. — These katabolic metamorphoses are intro¬ 
duced when a few unstaining globules arise in the substance 
of the yolk balls. These globules increase in number and size 
until the yolk ball assumes a vacuolated appearance (Figs. 215, 
217, 228). At the same time its ground substance loses its 
staining power and no longer stains homogeneously. At the 
commencement of these changes the yolk ball may even 
increase somewhat in size, since the substance of the globules 
is added to it. These changes continue until the yolk ball either 
breaks up into the mature yolk globules ( Yk . GY., Fig. 235), 
or first breaks into a varying number of larger pieces, and then 
each of the latter divides into yolk globules. The yolk globules 
are usually nearly spherical in shape, and though by no means 
equal in size are always larger than those of the other nemer- 
teans examined. 
During the prophasis each yolk ball is enveloped by a clear, 
structureless zone of cytoplasm ; but this surrounding zone is 
usually not noticeable around the larger yolk-ball fragments, 
and never around the mature yolk globules. 
As to the cause of the fragmentation of the yolk balls, I can 
find no sure explanation from the facts at hand. However, the 
appearance of the colorless fluid globules within their substance 
must have an important connection with these katabolic changes, 
since they characterize the commencement of this period of 
change. It would seem likely that these colorless globules 
represent a fluid constituent of the cytoplasm which has 
actively or passively been taken into the yolk ball, — perhaps 
from the clear cytoplasmic zone enveloping each yolk ball,— 
