PREDETERMINATION OF SEX 315 



ing, both sexually and by parthenogenesis. They state that Mr. 

 C. N. AinsUe found similar cases. 



Stevens has given a brief account of several forms in which 

 the same female individual produced both males and sexual fe- 

 males (Science, vol. 26, Aug. '07). The color relations between 

 the mother and her young are also noted. The facts recorded are 

 highly interesting since they suggest that there is here a case of 

 alternative color inheritance. In some cases the color appears 

 to be due to the sex of the individual, i.e., a specific effect is pro- 

 duced by the combination that gives a male. But in other cases 

 the results do not appear to conform to this relation, nor do they 

 seem explicable by the assumption that sex linked factors are 

 involved. They do suggest, however, as Miss Stevens pointed 

 out, that a condition of heterozygosis in regard to the color fac- 

 tors may exist, and if so, chromosomes other than the sex chro- 

 mosomes must be involved. But until further experimental work 

 has been done, as Miss Stevens herself had planned, the inheri- 

 tance of color in relation to sex inheritance is obscure. 



In the light of these results the single line theory seems to be 

 the most probable one for these species of aphids. The cyto- 

 logical work on the aphids has shown that there are but two sex 

 chromosomes in the female, i.e., the sex chromosomes are not 

 doubled, as in the phylloxerans, and without this doubling it is 

 not possible, at present, to suggest a way in which the two-line 

 scheme would work out. 



