R. Pearl.Biology and Eugenics.5i 
We may next consider in greater detail these factors influencing fecundity, 
taking firstThe Anatomical Basis of Fecundity. 
Since, as already pointed out, egg production obviously depends in part 
upon the presence of ova in a normal ovary, a question which demands 
consideration is the following:— 
To what extent are observed variations in fecundity (i.e., in the number 
of eggs laid) to be referred to anatomical differences. In other words does 
the ovary of a high producing hen with, for example, a winter record of 
from 75 to 115 eggs, contain a larger number of oocytes than does the 
ovary of a hen which is a poor producer, laying no eggs in the winter 
period and perhaps but 10 or 15 eggs in the year? 
To get light upon this question the observations to be described have 
been made. The object was to arrive at as accurate a relative judgment 
as possible regarding the number of oocytes in the ovaries of different 
individual birds. It is, of course, impossible practically to determine 
accurately the total absolute number of oocytes in the ovary. What can be 
done, however, is to count the number of oocytes which are visible to the 
unaided eye. While such results do not tell us, nor enable us to estimate 
with great accuracy, the total number of oocytes in the ovary, they do 
nevertheless throw interesting and useful light on the questions raised above. 
Some counts of this kind are shown in Table I. 
Table I. 
Showing the Number of Visible Oocytes in the Ovary of Certain Fowls. 
Case No.Bird No.Breed.Winter Production.Total Visible 
Oocytes. 
I8021Barred Plymouth Rock31228 
2801799 99 9901666 
3803099 99 990914 
4800599 99 9951174 
5136799 99 9932306 
6801899 99 9901194 
7800999 99 9902101 
8801099 99 9951576 
942599 99 99 •••01521 
103546White Leghorn542452 
11206799 99323605 
12345399 9901701 
13383399 9902145 
1452Cornish Indian Game131550 
IS7iFi Cross ...........................1062000 E 2