1911] SHULL—REVERSIBLE SEX-MUTANTS 355 
included under cases I-XII produced male offspring like themselves 
when they were used as male parents (but not when used as female 
parents). These have been called “genetic hermaphrodites,” 
to distinguish them from occasional genetic males which possess 
female organs as a purely somatic modification, and which I have 
therefore called ‘somatic hermaphrodites.”” These ‘somatic 
hermaphrodites”’ will be omitted from the discussion for the present. 
Under cases II and III it is shown that genetic hermaphrodites, 
of whatever origin, when self-fertilized, yield dimorphic progenies 
consisting of females and hermaphrodites, thus confirming the 
conclusions derived from the F,. This fact, together with the 
apparent relative ease with which males are made to exhibit the 
organs of both sexes, has been. accepted as conclusive evidence 
that the hermaphrodites (and therefore also the males) are heterozy- 
gous with respect to sex, and the females homozygous (SHULL 26). 
In this regard Lychnis dioica L. agrees with Bryonia dioica (Cor- 
RENS 6); with many species of Coleoptera, Orthoptera, Hemiptera, 
Diptera, Odonata, and perhaps also with Myriapoda and Arachnida 
(McCiuNne 19, WILSON 38-42, MorRGAN 20, 21, STEVENS 31-34, 
etc.); and with the nematode worms, Heterakis (BovERI 4) and 
Ascaris megalocephala (BorING 3). In man, GuyeER (16) has 
demonstrated that there are two types of sperms, and while the 
relation of one or other of these types to the type of the egg is 
unknown, there can hardly be a doubt that here also the female 
is homozygous and the male heterozygous.* 
Although these widely divergent groups of plants and animals 
agree in having homozygous females and heterozygous males, 
there may still be fundamental differences in the different groups, 
since there may be three different kinds of homozygotes, and 
Correspondingly different kinds of heterozygotes. This question 
* Heterozygous females have now been recognized in Abraxas (DONCASTER and 
Raynor ro, and Doncaster 8, 9), sea urchins (BALTzeR 1), canaries (DURHAM and 
Marryar 11), and in domestic fowl (BATESON 2, SPILLMAN 28, 29, GOODALE 12, 13, 
HacEpoorn 17, Peart and SURFACE 24, 25, STURTEVANT 37). GUYER (14, I5) 
Teports two types of sperms in both the guinea fowl and the common fowl, but these 
observations are out of harmony with all the genetic studies in which sex-limited 
characters of the Gallinaceae have been involved. The considerable difficulties 
encountered in the cytological studies on these species suggest the advisability of 
@ repetition of this work. 
