J. W. H. Harrison 11 



phylogenetically younger female zonaria and the results justified the 

 most optimistic expectations, for the brood was entirely composed of 

 males and intersexes. Once more only one explanation rises to one's 

 mind, viz. that, as a result of combining gametes both of high 

 " positive " potential, we have generated a cumulative potential in 

 the zygote high enough to secure maleness. On the other hand, the 

 fusion of gametes, one of high male possibilities and the other of 

 lower female powers, has induced a sex potential in the zygote of such 

 a level as to raise it away from the female level, high enough to 

 render it an intersex but not sufficient for maleness. Again, if theory 

 be consistent with fact, an examination of the sexual character of the 

 intersexes should betray, by the overw^helming nature of the female 

 leanings, that these intersexes were modified females, and such indeed 

 was the case. 



Still a crucial test is left ; if it be possible to incline all the females 

 so far from femaleness as " intersexuality," then it must be possible to 

 throw them wholly into the male condition. To make the trial we 

 have still older species to employ, and these were paired in the usual 

 combination of the older male with the female of later evolution. 

 Hirtaria males were mated with zonaria and the still younger graecaria 

 females ; the broods were successfully reared, and they comprised males 

 only. Now half of these males must be normal ones of sex chromosome 

 content XX\ but the other portion, males in every structural essential, 

 can only be in possession of chromosomes necessitating the sex formula 

 of the individuals in it being written XY'. In connection with this 

 it might be urged that selective viability had been at work suppressing 

 the female zygotes ; this cannot be so, for in carefully conducted experi- 

 ments all of the ova proved fertile, and were successfully reared to the 

 imaginal state. Another answer to such objections, if one were required, 

 is the presence of the intersexes in the families considered previously. 



Therefore, almost certainly, the experimental results make it im- 

 perative that sex should be deemed a matter of potency or potential, 

 the latter the preferable as supplying a better explanation of the 

 development of intersexes. Further evidence pointing in the same 

 direction may be deduced from the sex proportions of the reciprocal 

 crosses in every case ; in these no anomalies in sex ever appear. Males 

 and females alike make their appearance in their accustomed numbers 

 just as if the broods were those of pure species making their appearance 

 naturally. Let us consider how the potential theory works out here. 

 We pair zonaria male (younger) with hirtaria female (older). For 



