174 The Case of the Ctirrant Moth [ch. 



inhibiting factor may be thought of as able to suppress 

 completely the development of the character when that 

 character is heterozygous — introduced, to use that ex- 

 pression, as one "dose" only — but unable to suppress it 

 when it is homozygous, represented by a double "dose." 

 On the view that femaleness itself is the suppressing 

 factor one difficulty has to be considered. Just as disease 

 or removal of the ovaries may lead to the appearance of 

 male characters we should expect that such disease might 

 lead to the occasional appearance of colour-blindness in 

 females. I do not however know of such a case. It must 

 nevertheless be remembered that even the appearance of 

 male characters is itself by no means a regular consequence 

 of these lesions, and perhaps we need not regard the 

 difficulty specified as a serious one in the case of colour- 

 blindness. 



Sex and Spiiriotis Allelonwrphism: the Currant Moth. 



The next case of which I shall speak is one which has 

 been worked out in considerable detail, and I anticipate 

 that for a long time to come it must rank as a classical 

 experiment in all discussions as to the nature of sex. The 

 work in question was done by Doncaster and Raynor and 

 it relates to crosses made between the Geometrid moth 

 Abi^axas grossttlariata and its variety lacticotor (iii). 



Lacticolor was originally known as an exclusively female 

 form (see Plate I). The experimental crossings gave the 

 following curious series of results: 



1. Lacticolor % y. grossulariata $ produced /^^ $s and 

 $s all grossula^data. 



2. F^ grossulariata % x F^grossulariata $ gave grossii- 

 la7nata ^s and $s and lacticolor $s ; no ^s of lacticolor being 

 formed. 



3. Lacticolor $ x F^grossulariata Z gave all four possible 

 forms, namely gi^ossulariata $s and $s, and lacticolor $s 

 and $s. The lacticolor males were the first that had ever 

 been seen. 



