286 MAINi; AGRICULTURAI, EXPERIMENT STATION. I9I2. 



rate from the body mature germ cells. Feciinclit}' in the female 

 will depend upon the production of ova and in the male upon 

 the production of spermatozoa. In mammals 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 offspring. 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. 



Taking fecundity as above defined it is obviously a character 

 depending upon the interaction of several factors. In the first 

 place the number of ova separated from the body by a hen must 

 depend, in part at least, upon an anatomical basis, namely, the 

 number of ova present in the ovary and available for discbarge. 

 Further there must be involved a series of physiological factors. 

 The mere presence of an anatomically normal reproductive sys- 

 tem, including a normal ovary with a full complement of ova, 

 and a normal oviduct, lis not enough to insure that a hen shall 

 lay eggs, that is, exhibit actual as well as potential fecundity. 

 While comparatively very rare, cases do occur in which a bird 

 possesses a perfect ovary and perfect oviduct and is in all other 

 respects entirely normal and healthy, yet never lays even a sin- 

 gle egg dn her life time. Such cases as these prove (a) that 

 what we may call the anatomical factor is not alone sufficient 

 to insure that potential fecundity shall become actual, and (b) 

 that the anatomical and physiological factors are distinct, in 

 the sense that the normal existence of one in an individual does 

 not necessarily imply the co-existence of the other in the same 

 individual. 



A case of this kind is found in hen no. 805 1 hatched March 

 29, 1909, and killed for autopsy record August 24, 1911. This 

 bird had the secondary sexual characters of the female per- 

 fectly developed, and was entirely normal in other respects 

 (body weight, 2366 grams). This bird never laid an Qgg during 

 its life. The ovary was normal (fig. 450) and was of about 

 the size proper to a fully developed pullet just reaching the 

 point of beginning to deposit yolk rapidly in certain oocytes in 

 preparation for laying. While counts were not made this ovary 



