92 



CROSSING. 



+ -26w 



4- -26 



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

 breeding. These animals had one F x 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 N 



by repeated back crosses. 

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



This brings us to the work 

 of the Drosophila specialists. « 50 55 60 « » „ 80 & <* « «. * ™ * a,* 



Fig. 12. 



Variability in weight of 49 Japanese 

 dwarf mice, 75 large whites, and 60 Fl 

 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 tenninology 

 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 



n 



4ii 



i i 



L 



r41 



n 



*o«s ion « u m n w » « u vo o) rn to in o no in no*) no »s» 



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. 



