272 



LILIAN V. MORGAN. 



have produced offspring of the expected classes. Another female 

 of the same kind undoubtedly occurred in a mass culture of double 

 yellow females, for there were found in the. culture some yellow 



Parents 



Fertilized egg 



_FB 



cf 



fB 



Mosaic:- anterior parts 



fB 



posterior parts 



Eggs of mosaio 

 Spam of black male 



XX 



died 







XX YQ like XOC? (sterile) 

 mother like father 







Y0<5 died 



Eggs of F t 



Sperm of any male 



survives 



mother and 

 grandmother 



Ilka father 



XX XO rarely XX YO like XYC? (fertile) YYC? dies 



FIG. 2. Diagram showing parentage and constitution of the mosaic and of 

 the line of non-criss-cross inheritance. The components of the double chromo- 

 some are arbitrarily represented as attached at " left " end. 



males and cross-over males and females of classes to be expected 

 if a female heterozygous for yellow had been present in the culture. 

 The question as to whether the break occurs in the place of the 

 original attachment of the chromosomes has not been fully tested, 

 but so far there is no evidence of duplication or deficiency at either 

 end of the detached chromosome. 



CYTOLOGY. 



The genetic behavior of the line of flies having the two insep- 

 arable sex-chromosomes is in entire accord with the condition of 

 the chromosomes as seen in cytological preparations of yellow 

 females and of their rare wild type XX X sisters. Both of these 

 classes of females receive from the mother not a single X, but two 



