254 RAYMOND PEARL 



Calculating the coefficient of correlation between these two 

 variables, breeding index and germ dosage index, we get 



r = +0.012 ± 0.151, 



a value equal to zero, wdthin the errors of random samphng. 

 It thus appears that there is no relation between the repro- 

 ductive capacity (as here defined) of the alcoholized birds and 

 the total dosage to which their gametes were subjected in the 

 breeding season of 1915. 



IV. DATES OF HATCHING OF Fi CHICKS 



In order to deal critically with certain classes of data to be 

 presented in later sections of the paper it is essential to have 

 in hand the facts in regard to date of hatching of the chicks from 

 treated and control parents. The data on this point are ex- 

 hibited in table 4. In the last column of this table the distribu- 

 tion is given for time of hatching of the Fi chicks of the cross 

 Black Hamburg cf X Barred Plymouth Rock 9 hatched from 

 normal, untreated parents in the season of 1913. These chicks 

 are used as controls on the chicks from treated parents in cer- 

 tain later sections of the paper. 



The data presented in this tablt show that the greatest differ- 

 ence between any two lots of birds in mean date of hatching is 

 between the methyl cf X untreated 9 9 on the one hand and 

 the ether cf' X ether 9 9 on the other hand, and amounts to 

 9.44 days only. The difference is probably significant statisti- 

 cally, but there is no reason to suppose that it is significant 

 biologically. It is well known that differences in the date of 

 hatching may influence certain developmental and physiological 

 characteristics of chickens, and anyone who wishes to do criti- 

 cal experimental work with poultry must guard against com- 

 paring in any way lots of chickens having average hatching 

 date differing by large amounts (for example, a month or moi;3). 

 In the present case it is evident that all the chickens in these 

 experiments may for practical purposes be regarded as April 

 hatched. All of the writer's experience with poultry would 

 indicate that no significance is to be attached to such differ- 



