LYMANTRIA DISPAR 37 



inherited determiner with two 'weak' X-borne determiners 

 shifts the male (XX) toward femaleness. It follows, there- 

 fore, that the X-chromosomes must contain male-determin- 

 ing factors, 'strong' in the 'strong' and 'weak' in the 'weak' 

 races, and that the female-determiner also 'strong' in the 

 'strong' and 'weak' in the 'weak' races, is not to be found 

 in the X-chromosome but elsewhere. Goldschmidt has 

 adduced reasons for the view that the female-determining 

 factor is resident in the Y-chromosome. Thus sex in the 

 Gypsy moth, he suggests, is determined by a relational 

 balance between a maternally inherited (Y-borne) female- 

 determiner (F) and a male-determiner (M), of which one is 

 present in the female and two in the male, and which 

 is borne in the X-chromosome. Intersexes appear if in 

 a hybrid combination of M and F these sex-determining 

 factors are not properly balanced. Goldschmidt regards the 

 M and the F as being single genes for the reason that never 

 in thousands of crosses has any result been obtained which 

 would support any other conclusion. 



His results can be illustrated in simple fashion by the 

 following scheme: In the Gypsy moth the male has a sex- 

 chromosome constitution XX, while the female is XY. The 

 male-determining genes are resident in the X-chromosomes, 

 the female are in the Y and are therefore restricted to the 

 maternal line. But Goldschmidt gained evidence which 

 forced him to the conclusion that the female-determining 

 factors borne on the Y-chromosome acted prezygotically — 

 that is to say, before the X and the Y chromosomes in the 

 naturing egg had separated. The physiological effects of the 

 action of these Y-borne genes would thus pervade the whole 

 of the immature egg. Two kinds of eggs would be produced, 

 an X-bearing egg, the Y-chromosome having passed into 

 the polar body, or a Y-bearing egg, the X-chromosome 

 having passed into the polar body, but, in respect of the 

 female-determining reactions which result from the func- 

 tioning of the Y-borne gene, the X-bearing egg and the 

 Y-bearing egg produced by the same female are exactly 

 alike. 



A male like a female has its origin in an egg, but in the 



