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THE AMERICAN NATURALIST [Vol. XLV 



genes for the male and the male carries those for the 

 female. In fact, I am inclined to think that the evidence 

 forces us to accept Darwin's original view, that in each 

 sex the elements of the other sex are present ; a view that 

 has been largely given up by modern theorists (except 

 by Strasburger). I think that we must accept this in- 

 terpretation for several reasons. Every zoologist is 

 familiar with cases in which the same individual may at 

 first function as a male and later as a female. More re- 

 markable still is the case of the Nematodes in which in 

 some species the female has come to produce both eggs 

 and sperm as shown by Maupas and more recently by 

 Potts, while in another closely related species it is prob- 

 ably the male, according to Maupas and Zur Strassen, 

 that has come to produce eggs as well as sperm. There 

 is further the class of cases where the female develops 

 the male secondary characters and the male those of the 

 female. This class of cases I shall discuss later, for the 

 value of this evidence will turn on whether these second- 

 ary sexual characters are represented by independent 

 genes, or are expressions of the presence of one or the 

 other sexual condition ; or due to a combination of these 

 two possibilities. 



By means of the following formulae we can meet the 

 requirements that the situation seems to me to demand. 

 If we admit that in the first class one of the genes has 

 become larger than the other female genes, and if we 

 admit that in the second class one of the female genes 

 has become smaller than its sister genes we can account 

 for the results as the following f ormulae show : 



Fmfm Female Fm fm 



Ffmm ffmm 



FmFm Female Fm Fm 



Fmfm Male Fm \ f m 



female male 



