NUMBER OF OVA: ALBINO RAT 435 
On the number of ova in relation to age 
As was stated earlier, the total number of ova is greatest dur- 
ing the first days after birth, some ovaries containing as many 
as 35,105 ova. This number, however, decreases rapidly with 
increase of the ovaries in weight until it drops to about 11,000 
at twenty days. From twenty-three days to sixty-three days the 
total number of ova varies only slightly—that is, from about 
11,000 to 10,000. At about sixty-three days ovulation appears. 
The number of ova then decreases at first rapidly from about 
10,000 at sixty-three days to about 2,000 at 947 days. The 
variation in the total number of ova according to increasing ages 
is different from that in most other organs of the rat, as, for in- 
stance, in the brain, in which the number of cells not only in- 
creases during the earlier period of growth, but soon becomes 
nearly constant, the individual neurons persisting for the most 
part throughout the entire span of life. 
The progressive changes in the form of the graph (chart 2) at 
the different periods seem to be related to several factors, such 
as the new formation of ova, their degeneration, ete., and I wish 
to discuss these factors now. 
The new formation and the degeneration of ova 
According to Kingery’s observation on the white mouse (’17), 
the proliferation of cells from the germinal epithelium does not 
take the form of tubular down-growth, but the cells are grouped 
in irregular masses just beneath the epithelium. The cell masses 
are made up of oocytes and indifferent cells or future follicle 
cells. In the course of development some of the flattened adja- 
cent epithelial cells completely surround the oocyte which is 
still in the germinal epithelium. As growth proceeds, the other 
cells of the germinal epithelium extend up over this oocyte in its 
primary follicle, which is in this manner left behind in the tunica 
albuginea under the epithelium, and thus gradually passes 
through the tunica to reach the stroma beneath. 
Since my study was concerned principally with the ova num- 
ber and not with questions of the oogenesis, I am not prepared 
