430 HAYATO ARAI 
group with the smallest diameter (20 to 40 4) is most subject to 
degeneration, for the numbers in it fall most rapidly and con- 
tinuously. The group with the largest diameter (more than 60 yp) 
is most constant in number. ‘This relation does not necessarily 
mean that these largest ova persist for any long period, but 
merely that the balance between their formation and degenera- 
tion is rather evenly maintained. 
The first phase of the graph for the entire number of ova may 
be interpreted as due to the fact that during this phasemany 
primitive germ cells are growing rapidly, yet at the same time an 
excess of cells is undergoing degeneration, so that the number 
falls rapidly. 
From 8 up to 16.5 mgm. in ovary weight the enlargement of 
newly formed definitive ova is mainly responsible for the increase 
in the weight of the ovaries, containing a nearly constant number 
of ova. All the groups of ova more than 20 uw in diameter be- 
have in much the same manner. After such ova are first recog- 
nized there is a short period in which they increase in number, 
followed in each group by a more or less pronounced decrease to 
the end of the series. On the whole, then, the total number of 
ova decreases according as the ovaries grow in weight, and in the 
first phase this decrease is very rapid, but from a weight of 6.5 
mgm. it becomes much slower. 
The number of ova less than 20 uw in diameter is not plotted on 
this chart, but, as table 10 shows, it would give a curve practi- 
cally identical with that for the total number. 
The comparison of my own data on the weights of the ovaries 
with those given by Donaldson (’15) shows the following rela- 
tions according to age (table 11). 
So far as the critical periods for the data are concerned, there is 
good agreement beween the two determinations in table 11, but 
the last entry indicates that my animals were somewhat retarded. 
The data show that the weights of the ovaries hold an inverse 
relation to the number of ova, that is, the heavier the ovaries 
the fewer are the ova in them. This inverse relation may be 
due in part to the formation of the interstitial tissue, but de- 
pends mainly on several other factors, such as the corpora lutea, 
the number of well-developed follicles, degenerate follicles, ete. 
