NUMBER OF OVA: ALBINO RAT AT 
Comparison between man and the rat in regard to the postnatal 
changes in the ovaries 
It may be worth while to compare the results obtained from 
these studies on the development of the ovary in the rat with 
those in man, especially during the period in which the degener- 
ation of the primitive germ cells and the new formation of defi- 
nitive ova is most active. 
If we take sixty-five days as the mean age for the first ovula- 
tion, we find that the rat is distinctly precocious for sixty-five 
days, corresponds to about sixty-five months of human life, or 
roughly, five and a half years. According to Vierordt’s table, 
the first menstruation in man may occur in tropical countries 
at eight years, but more commonly a year or two later. 
On the other hand, the cessation of the breeding period in 
the female rat at eighteen to twenty months (= 45 to 50 years) 
agree very well with the appearance of the menopause which 
occurs in man between forty-five and fifty years. 
As is to be expected, individual rats may breed for a longer 
period, and King (715) has reported a female bearing a litter of 
one at twenty-two months and, as table 15 shows, the rat at 947 
days (= thirty-one months) fad newly formed corpora lutea 1 in 
its ovaries. 
SUMMARY 
1. The total number of ova in both ovaries was counted in 
thirty-nine albino rats ranging in age from birth to 947 days. 
2. In relation to the body weight the size of the ovaries in- 
creases to a maximum at 33 grams of the body weight, then de- 
creases up to puberty, after which it increases rapidly and reaches 
the second maximum. 
The ovary weight according to age shows continuous increase 
up to thirty-one months (table 12). 
3. The weight of the right ovary is less than that of the left— 
about 90 per cent—while the total number of ova in the right 
ovary is slightly more than in the left, though the difference is 
small (table 1). 
THE AMBRICAN JOURNAL OF ANATOMY, VOL. 27, NO. 4 
