92 



CROSSING. 



Chinese series, which were born in one litter and had the same 

 breeding. These animals had one Fj and one 

 Robertson parent. Although the data are not 

 sufficiently worked out to admit of more than a 

 general statement, it is clear 

 that they show evidences of 

 a complex factorial segrega- 

 tion, which is becoming 

 more and more simple the 

 further the genotypic consti- 

 tution of the hybrid stock 

 is made to conform to that 

 of one of the parent-species 

 by repeated back crosses. 

 (Fig. 12, 13, 14, 15.) 



This brings us to the work 

 of the Drosophila specialists. S5 M K * * 85 



Fig. 12. 



Variability in weight of 49 Japanese 

 dwarf mice, 75 large whites, and 60 F 1 

 animals. Weight expressed in percent- 

 ages of standard weight of white mice 

 as published by Robertson. 



In later years studies on inheritance 

 in these flies are as common in the lit- 

 erature on Genetics as articles dealing 

 with Oenothera around 1910. The Oeno- 

 thera specialists up to date of publication 

 of Herbert Nilsson's work were fast 

 developing a terminology 

 and a technique of their 

 own, which tended to cut off 

 these authors from the Gen- 

 eticians interested in ques- 

 tions of a more general na- 

 ture. The awe with which we 

 outsiders looked upon the 



Fig. 13. 

 Variability in F2 from the cross 



Japanese dwarf large white mice 

 weight expresses in percentage of 

 standard weight. Males and females 

 at four, five and six weeks. 



