162 EVIDENCE OPPOSED TO 



This theory would be quite compatible with the 

 belief that adaptive somatic sex-characters may be 

 due to external stimulation, for supposing that the 

 hypertrophy or modification is conveyed to the 

 determinants in the gametocytes, and was confined 

 to one sex, e.g. the male, then these determinants 

 would be modified in association with the sex- 

 chromosomes of that sex, and thus though after re- 

 duction and fertilisation they would be present in 

 the female zygote also, they would not develop in that 

 sex. Thus supposing M to represent a modification 

 acquired in the male and m the absence of the modi- 

 fication, such as the feathered antenna of a moth, and 

 the sex-chromosomes to be X and Y> then we should 

 have in the gametocytes 



Male Female 



MM mm 



XX XY 



Gametes. . MX, MX: mXmY 

 Zygotes . . MmXX male, MmX Y female, 



and the character M would only appear in the male 

 because it only develops in association with XX in 

 the somatic cells descended from the male zygote. 

 This would be the result in the first generation in 

 which a somatic modification affected the factors in 

 the chromosomes. In the next generation m in the 

 male would be affected, and the male for the sake 

 of simplicity might be supposed to become MMXX. 

 When the female gametes segregated, some would 

 always be mY, and some zygotes therefore MXmY. 

 Others might be MMX Y. On this theory, therefore, 

 there would always be some females heterozygous 

 for the male character. 



