NUMBER OF OVA: ALBINO RAT 421 
The percentage values for the number of ova with diameters 
from 40 to 60 uw increase rapidly from ten days to twenty days, 
at which age they reach an absolute maximum. ‘This in turn is 
followed by a rapid decrease till forty-one days. 
From forty-one days on to 947 days the percentage values re- 
main less than 2 per cent, except in three cases. ‘There seems to 
be, however, a slight tendency for the percentage values in this 
group to increase in the older animals. 
The ova more than 60 yu in diameter only once represent more 
than 2 per cent of the total and usually less than 1 per cent, so 
that no attempt is made to correlate the variations in their 
abundance with other changes. 
In this table are the determinations for four pregnant rats. In 
the ovaries from a rat pregnant at eighty days the percentage 
values of all ova with diameters more than 20 u are considerably 
higher than in the ovaries of non-pregnant rats, but in the re- 
maining three cases this peculiarity does not appear. Whether , 
this is a significant difference cannot at the moment be deter- 
mined. 
From table 4 it may be seen that in the ovaries in which cor- 
pora lutea are absent the mean number of ova per 0.1 mgm. of 
ovary weight tends to run inversely to the percentage value for 
the number of ova having a diameter of 60 uw or more, and a 
similar relation holds after the corpora lutea appear in the ovar- 
ies. It therefore follows that in the former cases the number 
of largest ova is in large measure responsible for the greater 
weight of ovary, while in the latter cases both the largest ova and 
the corpora lutea may be taken as the responsible factors. 
It should be stated that in young ovaries there are also many 
larger ova with diameters 40 to 60 u or more, though it is question- 
able whether these are mature because the layer of follicle cells 
is about three to four cells thick, and moreover the cavity is not 
yet formed. I am rather inclined to believe that these ova are 
in the first stage of degeneration rather than in a stage of de- 
velopment. After thirty days we find in the ovaries many 
well-developed follicles, which not only have a cavity, but many 
layers of follicle cells, and as in the mature follicles the cumulus 
