440 HAYATO ARAI 
fall. Following this rapid fall, the next period is represented by 
one of constancy from about twenty-three up to about sixty- 
three days. This period of constancy may be due to a balance 
between the degenerating cells on one hand and the newly formed 
germ cells on the other. Among the degenerating germ cells 
may be some of the germ cells of the second proliferation besides 
the primitive germ cells, and, though lacking evidence, I am 
inclined to believe that at this time the majority of the primitive 
germ cells have already disappeared. 
The statements made by Winiwarter and Sainmont and by 
Kingery that all primitive germ cells are degenerated, and the 
view of the two former investigators that all of the second pro- 
liferated germ cells have disappeared, may very likely apply to 
this prepubertal period in the rat as mentioned above. 
Following this period of constancy, the curve again shows a 
rapid decrease up to seventy days. Since during this period the 
corpora lutea begin to appear, we may assume that at this period 
also the cells are degenerating rapidly. Although even after 
puberty there is some new formation of oocytes, the sudden de- 
crease in the number of ova must be due to a great excess of the 
degenerating cells. 
Following this second rapid fall, the curve now shows a gradual 
decrease up to 947 days, though there occur some slight fluctua- 
tions, probably merely individual, especially at the earlier period. 
We may safely state that, though some few ova might be newly 
formed, the decrease in the total number of ova is due to the 
degeneration of the germ cells which represent those of the 
second proliferation. 
I wish to emphasize the fact that the degeneration of the prim- 
itive germ cells begins from one day after birth and continues up 
to about sixty-three days, at which time all of the primitive ova 
may disappear completely—a result which in general agrees with 
the observation of Kingery. 
Chart 2 also shows that the larger oocytes are relatively more 
numerous at an earlier age than at puberty. 
This relation may indicate that the primitive ova before pu- 
berty, especially at the earlier period, enlarge rapidly, and before 
