TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



sexual families. Here selective maturation seems to be out 

 of the question. Also, in a paper now in the press, Doncaster 6 

 shows that in a certain strain of Abraxas which has an odd 

 number of chromosomes in the female, and which shows a 

 tendency to produce all-female families, those unisexual 

 families are not due to a selective death rate, and the most 

 careful cytological work has shown that there is definitely 

 not selective maturation. In all these cases it seems certain 

 that zygotes with the chromosome content usually associated 

 with one sex have developed into adults of the opposite sex. 

 Such results have forced many workers to conclude that the 

 X chromosome is, to say the least, not wholly responsible for 

 the determination of the sex of the embryo. 



Goldschmidt, 7 still looking upon the X chromosome as 

 the carrier of a sex factor, has put forward a theory which 

 brings into line a remarkable number of facts. He suggests 

 that the sex factor has different strengths in different individuals 

 particularly in different varieties and species, and so does not 

 always give the expected result at fertilization. In order to 

 work out this hypothesis it is necessary to suppose that in part 

 of the animal world, e.g., Mammalia and Diptera, the X chromo- 

 some carries a factor for femaleness, whereas in Aves and 

 Lepidoptera it carries the factor for maleness ; and that in the 

 former groups the factor for maleness is carried by the Y 

 chromosome or possibly by the cytoplasm, while in the latter 

 groups it is the factor for femaleness which has this location. 

 This, of course, splits the animal world into two parts in an 

 arbitrary way. It is true that the split does exist cytologically, 

 the Mammalia and Diptera having the odd X chromosome 

 in the male, whereas in Aves and Lepidoptera it is found in the 

 female : but to suppose that in the former it carries femaleness 

 and in the latter maleness, seems to make the gulf even wider, 

 and suggests a state of affairs not easy to reconcile with any 

 idea of evolution. 



