J. W. H. Harrison . 265 



reared only four would be regarded as other than pure filigrammaria, 

 not even a specialist being able to detect the faintest indications of 

 autumnata. In the case of filigrammaria it has required two back 

 crosses to secure the passage back to that species. 



As for the four aberrant individuals they show very considerable 

 approach to the pseudo-mutants of the ^3 generation ; in fact, one of 

 them is precisely the same as those, and the other three only differ in 

 being decidedly darker. The same consideration of mitotic dislocation 

 is, in all probability, responsible for their appearance, because again in 

 the gametogenesis of the back cross between J^i $ and filigrammaria </• 

 we are dealing with a second hybrid generation ; the same interference 

 as we considered possible in the case of the F2 generation may be at 

 work here. If this be the case a preferential setting up of a deifinite 

 type of gamete, when such are aberrant, may conceivably result in 

 similar phenotypic if not genotypic manifestations. 



The Back Gross between F^ ^ and filigrammaria $ . 



This generation, except that we have the expected drop in mean 

 size toward filigrammaria, agrees with that obtained in the reciprocal 

 combination and cannot by any test save this one of size, which is cer- 

 tainly a matter of chance, be separated from them. Once more a single 

 back cross has failed to restore the filigrammaria condition. The very 



TABLE V. 



Summary of sex ratios in the Oporabia autumnata-filigrammaria 

 experiments. 



Culture 

 Oporabia autumnata from Pinewood ... 

 Oporabia autumnata hora Birchwood ... 

 Oporabia filigrammaria ... 



Fi Oporabia autumnata^ (from pine) x . filigrammaria ^ 

 Fi Oporabia autumnata -J (from birch) x 0. filigrammaria $ 

 F2 Oporabia autumnata ^ (from pine) x 0. filigrammaria $ 

 F3 Oporabia autumnata^ (from pine) x O. filigrammaria^ 

 Back cross 1 = Oporabia autumnata (pine) (J x i^j $ (pine) 

 Back cross 2= Oporabia filigrammaria ^ x Fi^ (pine) 

 Back cross 3 = F^J (pine) x Oporabia filigrammaria $ 

 Back cross 4 = Oporabia filigrammaria ^ x Back cross 2 $ 



obviously superior power of autumnata in this respect is very curious. 

 One would have thought that the heavier barring in a palpable case of 

 blending inheritance would have had. a greater effect than the feebler 

 state of autumnata in this respect, and that therefore there should have 

 been a speedier reversion to filigrammaria. But one must not forget 

 that autumnata is the phylogenetically older form and that filigram- 



