Abstracts. 305 



THE SELECTION PROBLEM.* 



This paper deals with the general problem, "Does selection 

 (in the sense of long continued selection) cause gradual changes 

 in the given plasm in the direction of selection." The evidence 

 when studied is found to prove just the opposite, that these 

 supposed careful selections are in reality chance selection of 

 favorable mutations. 



STUDIES ON THE PHYSIOLOGY OF REPRODUCTION 

 IN THE DOMESTIC FOWL. 



XVII. The Influence of Age upon Reproduction Ability, 

 WITH A Description of a New Reproductive Index.! 



The belief is widespread among poultry breeders that two 

 year-old birds or older should be used for breeding purposes. 

 The alleged reasons for this are superior vigor of the offspring 

 or more numerous progeny per mating, etc. This paper takes 

 up the points for the 1114 mating in the nine years' experience 

 of the writer. A mathematical measure of the reproductive 

 ability or fertility is introduced for this treatment. This New 

 Reproductive Index for Poultry is 



RI: 



Number of chickeiis alive at the end of the 3rd week 

 after hatching X 100 



Total number of days from the day when this mating 



began to the day when the last egg from this mating 



began its incubation. 



Treated in this way the following facts are brought out: 

 For the strain of Barred Rocks used, and under the con- 

 ditions of environment and management which obtained during 

 the experiments, the reproductive index has a mean value of 

 about 12 per cent. 



*This paper is an abstract from a paper by Raymond Pearl, having 

 the same title and published in the American Naturalist, Vol. LI, No. 

 602, pp. 65-91. 



fThis paper is an abstract from a paper by Raymond Pearl, having 

 the same title and published in Genetics, Vol. 2, pp. 417-432. 



