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SEX-LIMITED INHERITANCE IN INSECTS. 



By L. DoN'CASTER, Cambridge. 



It is now generally recognised by students of Mendelian in- 

 heritance that, of any pair of characters, the dominant character 

 is due to the presence of a "factor" which is absent in the 

 case of the recessive character. The essence of sex-liniitcd 

 inheritance is that the individuals of the sex in which sex- 

 limited transmission occurs transmit the positive ("present") 

 factor to oftspring of one sex only ; e.g., in the case of Abraxas 

 grossulariata, if G be the factor for grossidariata, g ( = absence 

 of G) that for lacticolor, then the heterozygous female Gg 

 transmits G only to her male offspring, thus : 



/\ 



gg^ GgS 



A heterozygous male, on the other hand, mated with a lacticolor 

 female transmits G to offspring of both sexes, thus : 



gg'^ X Gg¿ 



Gg^ gg'i Gg¿ 



It appears, in fact, that eggs in this species which will develop 

 into females can never bear (/, wild females having the con- 

 stitution Gg. 



In his recent papers on the inheritance of several characters 

 in Drosophila a)npclophila. Prof. T. H. Morgan has shown the 

 existence of sex-limited inheritance of the converse type, in 

 which it is the male which always transmits certain characters to 

 his daughters ; e.g. a white-eyed male appeared in his cultures, 

 and from this a white-eyed strain was built up. It then 

 appeared that when a normal (red-e}ed) male \\a> mated with 



