1gr1] SHU LL—REV ERSIBLE SEX-MUTANTS 331 
generation, and two explanations seemed possible: (1) these two 
types of hermaphrodites might be respectively homozygous and 
heterozygous in regard to a modifying factor H, whose presence 
was assumed, on the suggestion of CorRENS, as possibly necessary 
for the change of a normal male into a hermaphrodite; (2) the 
hermaphrodites of the second type (C and D), which gave first 
generation progenies equivalent to those produced by normal males, 
might owe their hermaphrodite character to some accident of 
development which affected the soma alone, leaving the germ cells 
unchanged. In this case they might be appropriately called 
“somatic hermaphrodites,” to distinguish them from those of the 
first type (4 and B) which transmitted the hermaphrodite char- 
acter to their male offspring and which are therefore to be recog- 
nized as “genetic hermaphrodites”’ or true hermaphrodite mutants. 
Neither the character of the females nor the relationship of the 
two types of hermaphrodites could be determined from the results 
of the first generation, but it was obvious that at least a partial 
solution could be expected from the second generation. To attain 
this end a large number of crosses were made in 1909, by using 
hermaphrodite individuals and their derivatives in various com- 
binations with each other, with unrelated females, and with normal 
males. The offspring of these crosses were grown during the sum- 
mer of 1910, and the 104 families produced from them included 
6132 individuals which came to bloom and of which the sex was 
tecorded. These records were made in the writer’s absence by Mr. 
R. Cattin Rosz, to whose energy, faithfulness, and care it gives 
me pleasure to testify. 
In order to comprehend fully the problems involved, it will be 
advantageous to consider some assumptions which were permitted 
by the results of the F, crosses, and whose availability is partially 
tested in the F, families reported in the present paper. In this 
Connection it is also important to consider briefly the “presence 
and absence” hypothesis, a full discussion of which, however, 
Would require too great a digression. Although this so-called 
hypothesis is frequently referred to by students of genetics, I am 
not aware that it has ever had a very definite formulation, and it 
would undoubtedly be defined differently by different students. 
