SEX INHERITANCE 113 



single factor difference distinguishes the two species 

 in regard to the spot. Tlie factor pair is not sex- 

 hnked, and is, therefore, autosomal. In other 

 insects it has been shown by castration experiments 

 that the development of the secondary sexual 

 characters is not dependent on the presence of 

 the gonad and if this relation holds also for Euchistus 

 the factors must be supposed to produce their 

 effects or not, according to the sex of the individual 

 in which they occur. 



Besides the above case of sex-limited characters 

 in a wild species we have several cases among the 

 mutant races of Drosophila melanogaster. These 

 mutants are characterized by a greater effect of a 

 gene on one sex than on the other, just as with the 

 horns of certain races of sheep. Among mutants 

 of this type are eosin, facet, and cut. Certain 

 mutations produce a visible difference in only one 

 sex; thus ''side-abnormal" is distinguishable only 

 in females, the males being entirely normal in 

 appearance. A different type of this class is that 

 in which the mutation affects some distinctly male 

 or female organ such as "twisted penis," or ''closed 

 ovi]:)ositor." Certain mutant races also are entirely 

 sterile in one sex but show a normal fertility in the 

 other sex. Thus ' ' cleft ' ' and ' ' giant ' ' are male-sterile, 

 while morula, fused and dwarf, are female-sterile. 



In certain butterflies there are several types of 

 females but only one kind of male. It has been 

 shown by Puimett and others that such a state of 

 affairs is explicable on Mcndelian principles if we 



