INHERITANCE OF FECUNDITY 165 



The 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, 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 question 

 raised above. 



The counts of the visible oocytes for a number of birds are given 

 in table 4. These counts were made at my suggestion by my 

 assistant, Miss Maynie R. Curtis, to whose painstaking care and 

 skill in carrying through the tedious business of counting it is a 

 pleasure to acknowledge gratefully my indebtedness. Prof. W. 

 F. Schoppe of the University of Maine is carrying this work for- 

 ward and later we hope to be able to publish more extensive data. 



space, and the manifoldness in respect to method, of the experiments upon which 

 this discussion is based are so great and the checlcs on this point have been so 

 numerous as to make it quite certain that the results are not influenced by a differ- 

 ential effect of the environment, arising from individual preferences of birds for 

 particular sorts of food, or other similar peculiarities of behavior. When a result 

 is stated to be due to inheritance the reader may assume, even though a specific 

 statement is not made to that effect, that careful, critical consideration has been 

 given to possible environmental influences. 



