94 Nature of the Genetic Material 



males and in females of special genetic constitution, a mosaic eflFect 

 is observed (see Goldschmidt and Poppelbaum, 1914, and Poppel- 

 baum, 1914). In the extreme this occurs in the triploid intersexes of 

 Solenobia (Seiler; see his final discussion, 1949) in which all (?) 

 the intersexual development is of the mosaic type. This means that 

 each cell has only the alternative female or male (as also in the non- 

 mosaic type) but that the decision of this alternative at the time of 

 the turning point requires a threshold condition, which in the mosaic 

 type is not reached in all cells. The consequence is that a more or 

 less large number of cells remain as they were, while the others 

 change their sexual development, closely parallel to the mottled eyes 

 of Drosophila. The fact is best seen in wings of intersexual Lymantria 

 males (or females of special genetic composition) in which some 

 groups of scales remain male while others turn female; or in the geni- 

 tal ducts of intersexual Solenobia (Seiler) in which a mosaic of patches 

 of the very difiPerent female and male type epithelium appears. In both 

 cases the amount of mosaic spots with the changed sex character 

 increases with intersexuality (i.e., earlier turning point). The parallel 

 effect in Drosophila is increase of white spots when the quantity of 

 heterochromatin changes. It is very tempting to parallel the two 

 sets of facts by saying that the different potencies of sex determiners 

 in diploid intersexuality {Lymantria) which control the amount of 

 mottling and the different quantities (via numbers of chromosomes) 

 in triploid intersexuality ( Solenobia ) are in fact differences in hetero- 

 chromatin. This means that the sex determiners involved are blocks 

 of heterochromatin. I consider these facts and their analysis to be a 

 very important asset to the view presented here. 



