112 MENDELISM chap. 



on the same lines as the grossulariata and lacticolor 

 patterns of the currant moth, but with one essential 

 difference. The factor which repels the red-eye 

 factor is in this case to be found in the male, 

 and here consequently it is the male which must 

 be regarded as heterozygous for a sex factor that 

 is lacking in the female. 



In order to bring these cases and others into 

 line an interesting suggestion has recently been 

 put forward by Bateson. On this suggestion each 

 sex is heterozygous for its own sex factor only, and 

 does not contain the factor proper to the opposite 



sex. The male is of the 

 Mmff Ffmm constitution tJ/^^/)^ and the 



gives gives -'-' 



gametes gametes female Ffmm. Each sex 



'^ ^ /ml productive produCCS tWO SOrtS of 



mf ^Fm/ fertilisations gametes, J// and 7«/ in 



5^ ZZ^/rifeSltioLT the case of the male, and 



Fm, fm in that of the 

 female. But on this view a further supposition is 

 necessary. If each of the two kinds of spermatozoa 

 were capable of fertilising each of the two kinds of 

 ova, we should get individuals of the constitution 

 MmFf and mmff, as well as the normal males and 

 females, Mmff and Ffmm. As the facts of ordinary 

 bisexual reproduction afford us no grounds for 

 assuming the existence of these two classes of indi- 

 viduals, whatever they m9.y be, we must suppose that 

 fertilisation is productive only between the sperma- 

 tozoa carrying M and the ova without F, or between 

 the spermatozoa without M and the ova containing 

 F. In other words, we must on this view suppose that 

 fertilisations between certain forms of gametes, even 



