EGG PRODUCTION. 8 1 



several separate and independently varying sets of factors. The 

 unit of such statistics is the individual offspring at birth. But 

 the production of an individual offspring by a viviparous animal 

 implies (i) the removal of an ovum from the ovary (ovulation) , 

 (2) the fertilisation of this ovum, and (3) its successful 

 development in utero. A considerable proportion of partial or 

 complete sterility in mammals is the result of a. failure of the 

 ovum to be fertilized, this failure in no wise depending in many 

 cases on any fault of the ovum itself. The true innate fecundity 

 of the female organism is clearly measured by capacity for 

 ovulation. This is primary, and the other factors concerned 

 in the production of an individual organism are secondary, in 

 so far as the measurement of fecundity is concerned. 



In view of these considerations it seems desirable to make 

 use of a more precise terminology than that commonly employed 

 in discussing these matters. We would suggest that the term 

 "fecundity" be used only to designate the innate potential repro- 

 ductive capacity of the individual organism, as denoted by its 

 ability to form and separate from the body mature germ cells. 

 Fecundity in the female will depend upon the production of ova 

 and in the male upon the production of spermatozoa. In mam- 

 mals it will obviously be very difficult, if not impossible, to get 

 reliable quantitative data regarding pure fecundity. On the 

 other hand we would suggest that the term "fertility" be used 

 to designate the total actual reproductive capacity of pairs of 

 organisms, male and female, as expressed by their ability when 

 mated together to produce (i. e. bring to birth) individual off- 

 spring. Fertility, according to this view, depends upon and 

 includes fecundity, but also a great number of other factors in 

 addition. Clearly it is fertility rather than fecundity which is 

 measured in statistics of birth of mammals. The terms 

 fecundity and fertility will be used as here defined by the 

 present authors in future discussions of their work. 



As has been pointed out the results of the present investiga- 

 tion do not indicate that there is a sensible inheritance of 

 fecundity from mother to daughter in the mass. Of course, it 

 is not proposed to let the matter rest here; this result will be 

 tested in every possible way. In particular it is important to 

 determine the correlation between mother and daughter in 



