92 



CROSSING. 



N 



hFi 



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

 breeding. These animals had one F^ 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. 



R 



7-25w 



J+-26W 4-26 I 7-25w 



« so 55 60 65 7D 



n 



4x[l 



-L 



e «a n n so as < 



Fig. 13. 

 Vaxiability 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. 



n 



73 BO 85 QO 9S 100 -IS 110 715 12DH 



Fig. 12. 

 VariabDity 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 speciaUsts 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 



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ta uo us >w MS ae iK% 



