No. 642] VARIATION IN SEX CHARACTERS 



57 



and absence of one X leaves a surplus of genes that work 

 in the same or in the opposite direction from that of the 

 mutant in question. 



Thus, by studying three kinds of eflfects, first, the 

 character complexes that result directly, secondly, the 

 exaggerations of the mutant characters whose genes are 

 in the same section or chromosome as that involved in the 

 loss, and thirdly the exaggerations of mutant characters 

 whose genes are in other regions, we can analyse roughly 

 the kinds and the signs of the genes that are in the region 

 in question. 



Since sexual and sex-limited characters are shown to 

 rest on tho same gtmctic basis, namt'ly. a preponderance 

 within the X of the plus oi- \hr minus niodibers of those 

 characters, it may l)e ([Ut^st ioned whetlu r there is any real 

 differenee between the>e two eate^-ories. If the race of 

 the nnitant eo>in were to become t'.-tablished in nature, a 

 systematist wouhl eeilainly inelude this ditference in 

 eye-color anion- his sexual di ft'ereiiees. t am of the 

 opinion that there is no dilTerenee lu'tween these two cate- 

 gories exeei)t that we call those sexual that are most 

 closely connected with re])roduetion. 



There is one strikin- .lifferenee between haj-loidy for 

 X and haploidy for an aut.»onie namely, that the 

 changes connected with ha]iloid>- foi- auto>onies are rela- 

 tively more uunu'rous and extreiiu'. ilaph.idy for the 

 second or third autosomes probably produces changes so 

 great as to be lethal, while haploidx' foi- the very small 

 l*(mrtli-cliromosome produces ehanuvs comparable in ex- 

 tent to all those of the male aside fi-oni the reproductive 

 organs. The proj.ortion of sex limited mutant charac- 

 ters is only about a tenth of the total, wliile X contains 

 about a (piarter of the ,uvnes. Sinei' the changes in char- 

 acter produced by absence of an X are relati\-ely small, 

 the internal balance of the X must be n'latively higli. 

 For a high i)i-oportion of the characters of the animal, the 

 ])his and minus modiliei's in the X nnist l)e in about the 



The comparison Just nia.h- between the effects of hap- 

 loidy for an aut.. sonic and the effects normally present m 

 di.ecious >cx show- that they have similai- uviiic bases - 

 munely. each is due to difference> in the ratio between two 



