184 RAYMOND PEARL 



One convention which is used throughout in the tabulation of 

 the material should be explained. In case a bird has a winter 

 egg record of exactly 30 eggs, she evidently falls on the boundary 

 line between the two fecundity classes already discussed and 

 defined (p. 172). The number of such cases is not large, but in 

 order to be perfectly impartial in their treatment it was decided 

 to split such a bird in two, in a metaphorical sense, and credit 

 one-half of her to the ' Over 30' winter fecundity class, and the 

 other half to the 'Under 30' class. This explains the fractional 

 records which occasionally appear among the frequencies in what 

 follows, and which might otherwise puzzle one used to thinking 

 of a hen as an individual unit, at least during the fecund portion 

 of her existence. In calculating the mean winter production (in 

 eggs) of the several classes these few birds with records of exactly 

 30 eggs have been omitted altogether. There are obviously two 

 equally fair ways of dealing with them in getting these averages. 

 One is to include each one in both ' over' and ' under' classes ; the 

 other is to include each one in neither class. The latter alternative 

 is adopted because simpler. 



Barred Plymouth Rock matings 



The data will be presented for each gametic constitution 

 separately. The analysis indicates that out of the 9 theoretically 

 possible types of male Barred JElocks shown in table 5 only six 

 have actually ever been used in the breeding pens. These six 

 classes of males represented in the data are classes 1, 2, 3, 4, 7 

 and 8. 



In any particular case it is practicable to determine the gametic 

 constitution of a male bird in respect to fecundity only through an 

 examination of the records of his daughters. To distinguish 

 different gametic types of males through analysis of the male 

 progeny, while theoretically simply, is practically not feasible 

 while any other investigations are going on. In order to deter- 

 mine the gametic constitution in regard to fecundity of the cock- 

 erels from a particular mating it would be necessary to rear 

 to maturity a reasonable number (5 to 10) of these males, and 



