252 RAYMOND PEARL 



cular degree of fecundity constantly reappears generation after 

 generation, the 'line' thus 'breeding true' in this particular. 

 AVith all birds (in which such a phenomenon as that noted under 

 h occurs) kept under the same general environmental conditions 

 such a result can only mean that the character is in sorqe manner 

 inherited. 



The facts set forth in paragraphs 1 and 2 have been presented, 

 and, I believe, fully substantiated bj'' clean-cut and extensive 

 evidence, in previous papers from this laboratory. In the pres- 

 ent paper it is further shown that : 



3. The basis for observed variations in fecundity is not anatom- 

 ical. The number of visible oocytes on the ovary bears no defin- 

 ite or constant relation to the actually realized egg production. 



4. This can only mean that observed differences (variations) 

 in actual egg productions depend upon differences in the com- 

 plex physiological mechanism concerned with the maturation of 

 oocytes and ovulation. 



5. A study of winter egg production (taken for practical pur- 

 poses as that from the beginning of the laying year in the early 

 fall to March 1) proves that this is the best available measure of 

 innate capacity in respect to fecundity, primarily because it 

 represents the laying cycle in which the widest difference exists 

 between birds of high fecundity and those of low fecundity. 



6. It is found to be the case that birds fall into three well- 

 defined classes in respect to winter egg production. These in- 

 clude (a) birds with high winter records, (6) birds with low winter 

 records, and (c) birds which do not lay at all in the winter period 

 (as defined above). The division point between a and b for the 

 Barred Plymouth Rock stock used in these experiments falls at a 

 production of about 30 eggs. 



7. There is a definite segregation in the Mendelian sense of the 

 female offspring in respect to these three fecundity divisions. 



8. High fecundity may be inherited by daughters from their 

 sire, independent of the dam. This is proved by the numerous 

 cases presented in the body of this paper where the same propor- 

 tion of daughters of high fecundity are produced by the same sire, 

 whether he is mated with dams of low or of high fecundity. 



