50 Effects of Alcohol on Selenia bilunaria 



commence life with a weighty advantage in that respect over the pro- 

 geny of untreated lots which have undergone no similar process of 

 selection. 



The second part demands more consideration. Throughout the lives 

 of the parent insects their germ cells have been constantly liable to 

 injury from the alcohol vapour. Now, as Pearl suggested, almost 

 certainly the germ cells will not be alike in resistive powers, and there- 

 fore the alcohol will not affect all in a similar manner. Merely con- 

 sidering the germ cells as acted on by a medium dose of alcohol, there 

 are three possibilities: (1) that weaker germ cells can be destroyed 

 or rendered wholly ineffective; (2) that more vigorous ones can be 

 weakened ; (3) that germ cells of the Grade I type can be so refractory 

 as to be quite unaffected. Clearly, too, by increasing the dose of 

 alcohol we could progressively eliminate all three classes. Supposing 

 that the amount employed in the present experiment was just sufficient 

 to destroy the feebler and medium members of the germ cell popula- 

 tion, what would that lead to ? It would only leave the most superior 

 to continue the race. If, as seems undoubtedly the case, an "A 1 " germ 

 cell population guarantees "Al" zygotes, then the subsequent genera- 

 tion should all be " Grade 1." And this exactly fits in with the insects 

 reared from the cross between a treated male and an untreated female. 

 Every single imago of this parentage was vastly superior to all controls. 

 Therefore selection, in the first place of first quality parents producing 

 the finest type of germ cells, followed by intense selection amongst 

 these chosen germ cells themselves, affords an adequate explanation 

 of the circumstances of this brood. 



If, however, the weaker cells alone are inactivated, and the stronger 

 and medium left, the former absolutely uninjured and the latter affected 

 in varying degrees, then the zygotes resulting from gametes so differ- 

 entiated would be of two grades : (1) composed of sturdy individuals 

 much the same as what we have just considered in the case of the 

 previous mating; (2) including distinctly less vigorous examples. This 

 agreed precisely with the state of affairs in the insects raised from the 

 pairing of an untreated control male and an alcoholised female. 



From the foregoing it will be perfectly obvious that, despite the 

 fact that both alcoholised males and females received the same dose of 

 ethyl alcuhol and for the same time, the conditions of the broods 

 from reciprocal crosses in which these insects took part were utterly 

 dissimilar. It therefore follows that, as far as these insects are 

 concerned, the gametes of the female are much less susceptible to 



