432 HAYATO ARAI 
numbers of ova tend to be similar in both ovaries, even in the 
cases where the total number is markedly low (see 198 day rat 
in table 1 as the extreme instance), Approximate equality is 
also found for the numbers of ova on the right and left sides if 
the means of the values for the low records at 80, 100, 110, 198, 
and 262 days are compared. These are: right ovary 2223 and 
left ovary 2357. 
The growth of ovary in weight according to age 
The growth of the ovary of the albino rat after birth has been 
studied by Jackson (’13) and Hatai (’13, ’14), and it shows sev- 
eral phases. Jackson, who constructed a chart showing the rela- 
tive weight of ovaries on body weight, pointed out two of these; 
the first phase beginning at birth showing an increase to a maxi- 
mum at a body weight of 10 to 15 grams, followed by a decrease 
up to a body weight of 60 grams. At 60 grams a second period 
of acceleration, which corresponds to the advent of puberty, 
begins, and during this phase the ovaries increase to a second 
maximum at 110 to 120 grams in body weight. After this the 
relative weight steadily decreases. ‘To make a comparison with 
Jackson’s results I have prepared table 12. 
This shows that according to my data the relative weight of 
ovaries increases to the first maximum at a body weight of 22 
to 33 grams, and then decreases gradually until a body weight 
of 95 grams. After 95 grams the curve rises rapidly at 102 grams 
in body weight. About this time corpora lutea appear in the 
ovaries, and the maximum relative weight is reached at a body 
weight of 142 to 161 grams, after which it decreases. In general 
the two sets of observations agree. 
The disagreement in the exact periods of the maxima between 
Jackson’s data and my own may be caused by the smaller num- 
ber of rats (thirty-nine) used by me. The explanation as to the 
true significance of the two maxima is difficult, especially the first 
maximum, owing to the complexity of the factors which enter 
into the growth of ovaries, such as the enlargement of follicles, 
the increase of stroma tissue, ete. The cause for the second 
maximum may be interpreted as follows: 
