PEARL— SEX RATIO IN DOMESTIC FOWL. 419 



lOOcfcf 



R. 



&d^ + d^cJ' 



for any mating, group or population. To convert any such sex 

 ratio into the form where the proportion of the sexes is expressed 

 as number of males per loo females one has only to divide the 

 given R by lOO — R , and the answer, multiplied by lOO, will be 

 the result sought. 



III. The Normal Sex Ratio in the Fowl. 



In dealing with sex ratios with the single mating or family as 

 the unit it is evident that the absolute size of the family from each 

 mating is a factor which must be considered. In a family of 2 the 

 only possible values for R ^ are o, 50, and 100 per cent. Again, a 

 single family of 2 is a very small sample of the gametic population 

 of the parents. The larger the family, obviously, the better the 

 sampling. Now in the usual method of dealing statistically with 

 sex ratios, where one simply counts all the males and all the females 

 in the population, no account whatever is taken nor can be, of the 

 badness of the gametic sampling in case of very small families. A 

 male in a family of i counts as significantly toward the final result 

 as a male in a family of 30. Yet it is quite sure that if we deter- 

 mined the sex ratio of the population on the basis of families of i 

 only, the result would be less worthy of confidence (i. e., of a larger 

 "probable" error) than if it were based on large families only. 



Tables I. to III. inclusive give the distribution to the sex ratios 

 for all fertile matings of the domestic fowl made by the writer in 

 the eight years from 1908 to 191 5 inclusive. Sterile matings are, 

 of course, not included. The data are divided between the three 

 tables on the basis of size of family. Table I. includes only families 

 in which 10 or more chicks were produced. Table II. includes fami- 

 lies of from 4 to 9 chicks, and Table III. covers the very small fami- 

 lies of I, 2, or 3 chicks only. In order that there may be no mis- 

 understanding it will be well to state clearly just the significance 

 of these tables. To take an example: The entry 2 in the first row 

 of Table I. means that in the year 1908 there were produced 2 fami- 

 lies, each containing 10 or more chicks, in each of which families 



