220 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 



five and six thousand individuals. Out of these records, the 

 following facts clearly appear.^ 



1. The record of egg production of a hen, taken by itseli 

 alone, gives no definite, reliable indication from which the prob- 

 able egg production of her daughters may be predicted. Further- 

 more, mass selection on the basis of egg laying records of females 

 alone, even though long continued and stringent in character, 

 failed completely to produce any steady change in type in th< 

 direction of selection. 



2. Differences in egg producing ability are, in spite of the 

 above results, certainly inherited. There are two lines of evi- 

 dence showing that this is the case. The first is that derived 

 from the general observation that there are widely distinct and 

 permanent (under ordinary breeding) differences in respect to 

 egg laying ability between different races, strains and breeds of 

 fowls. In the second place, a study of pedigree records of 

 poultry at once discovers blood lines in each of which a definite 

 particular degree of egg producing ability constantly reappears 

 generation after generation, the "line" thus "breeding true" 

 in this particular. With all birds kept under the same general 

 environmental conditions such a result can only mean that the 

 character is in some manner inherited. 



3. The number of visible oocytes on the ovary bears no 

 definite or constant relation to the actually realized egg produc- 

 tion. 



4. This can only mean that observed dififerences (varia- 

 tions) in actual egg production depend upon differences in the 

 complex physiological mechanism concerned with the develop- 

 ment of oocytes, and the separation of them from the ovary 

 and the body (laying). 



For reasons which cannot be gone into fully here on account 

 of lack of space, attention has been focused during the later 

 phases of the study, on winter egg production. 



Primarily these reasons are two : first, that winter produc- 

 tion is economically the most important in the case certainly of 

 poultrymen in northern latitudes ; and second that winter pro- 

 duction gives a more accurate and reliable measure of the bio- 



^More detailed discussion of these results, together with direct refer- 

 ences to the evidence on which they are based will be found in Bulletin 

 205, pp. 377-391. 



