IQII] 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 x . 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 

 (McCLUNG 19, WILSON 38-42, MORGAN 20, 21, STEVENS 31-34, 

 etc.); and with the nematode worms, Heterakis (BOVERI 4) and 

 Ascaris megalocephala (BORING 3). In man, GUYER (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. 4 



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 



4 Heterozygous females have now been recognized in Abraxas (DONCASTER and 

 RAYNOR 10, and DONCASTER 8, 9), sea urchins (BALTZER i), canaries (DURHAM and 

 MARRYAT n), and in domestic fowl (BATESON 2, SPILLMAN 28, 29, GOODALE 12, 13, 

 HAGEDOORN 17, PEARL and SURFACE 24, 25, STURTEVANT 37). GUYER (14, 15) 

 reports 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 

 a repetition of this work. 



