SEX INHERITANCE 113 
single factor difference distinguishes the two species 
in regard to the spot. The factor pair is not sex- 
linked, 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 
ovipositor.”’ 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 Punnett and others that such a state of 
affairs is explicable on Mendelian principles if we 
