No. 609] 



THE THEORY OF THE GENE 



529 



showed the least amount of notch, changed, after a few 

 generations, the outward character of the notch stock so 

 that at least half of those females that carry the notch 

 gene came to have normal wings. It might have seemed 

 that the gene itself had changed, possibly through con- 

 tamination with the normal gene, were such a thing pos- 

 sible. On the contrary, if these females with normal 

 wings are outcrossed to a male of any other stock, all the 

 daughters that carry the notch gene have the notch in the 

 original (atavistic) condition, showing that the gene still 

 acts in all its original strength. Moreover, suitable ex- 

 periments have shown that as a result of selection, a 

 modifying gene, already present in the original stock, has 

 been isolated. This gene modifies notch (although it 

 produces no visible effect on the normal wing) in such a 

 way that the notch is less likely to appear. The evidence 

 furnishes the twofold demonstration that the gene for 

 notch has not changed through contamination, and that 

 there is present a new and definite gene that does account 

 for the change. 



il)) Mriluuls nf I nhrni llnil arc unf MmdrVian. 

 It lias l)oen claim. Ml that >rcn(lcliaii iiihcritan.v is only 

 one kin.l of inheritance and apiflics to (mly a limited 



not be inherited in this wav becanL. it i> aftiimied. evohi- 

 tionary character, are iiot like Men.b-lian character^. 

 It is known tliat certain plastid.. >ucli a- .-hloropla^s 

 that lio in the pi'oto])1a>m are tran>nntted a> a rnle only 

 tlirono-h the egu' protoplasm. There can lie no donbt 

 that thi> <ort of transmission takes pla<-e. In principle it 

 is n.ot different from the transmission of certain kind< of 

 l)acterial di<ea>es like that of pebrine in the eo-o. of the 

 silkworm motli. Any inclnnon i,, the cyfo],lnHn .'apahle 

 of increasing there by .livision would' be medianically 



