8 Studies in the Hybrid Bistoninae. IV 



which, for the hybrid, suffices to cause it to appear as a male. And 

 this necessitates the acceptance of the corollary that the male sex gene 

 or determiner in hirtaria exceeds in power the corresponding factor or 

 chromosome in zonaria. 



Now this prepotency may, conceivably, be brought about in two 

 ways; either by the gross physical factor of mere size acting as a 

 twenty gram brass weight weighs down and thus overpowers a similar 

 ten gram weight, or it may rather be a matter of intensity of action 

 working somewhat as a small platinum weight turns the beam against 

 a brass weight of double its size. 



If the former be the case, then a cytological examination of the 

 chromosomes of hirtaria and of zonaria should produce evidence cor- 

 roborative of the point. Make the necessary examination, and what 

 do we find? We discover that the haploid chromosome number of 

 hirtar-ia is 14 and that of zonaria 5G, the individual chromosomes of 

 hirtaria being nearly always larger than those of zonaria. But note 

 the significant figures of 14 and 56. The ratio between these numbers 

 is 1 : 4 and it would imply that the chromosomes of hirtaria are com- 

 plexes, each carrying genes equivalent to those borne by four of 

 zonaria. 



From this one must conclude that only part of one hirtaria chromo- 

 some provides the mechanism of the sex determination. But it is not 

 impossible that one of the larger zonaria chromosomes and one of the 

 smaller ones of hirtaria are those responsible for the sex determination, 

 and in size these are so nearly alike as to remove any impression that 

 size alone will account for the preponderating influence of the hirtaria 

 male factor. Nor is this incompatible with the significance of the 

 figures 14 and 56, for it seems quite possible that the complexes of 

 hirtaria are not invariably groups of four units — if we term a zonaria 

 chromosome a unit. There are more methods of making four than by 

 adding together two and two I 



In my opinion, the balance of the evidence indicates that we must 

 look to the intensity of the sex factors for an explanation of the 

 aberrant results. 



Now this may be merely a case of the stronger force of a hirtar'ia 

 X chromosome overcoming that of the weaker Y from zonaria ; on the 

 contrary, it may be that sex is a matter of potential, and that in the X 

 and Y chromosomes of any given being we are concerned with some- 

 thing of a nature comparable with positive and negative electricity. 

 In an ordinary pur.e species we can regard the X chromosome as 



