J. W. H. Harrison • 35 



the Y interfere with one another, then the daughter cells are of com- 

 position XX' and X Y. In both cases the result is the same ; we have 

 adjacent to one another groups of cells, one of the male type XX' and 

 the other of forms, XY and XX' Y, of female possibilities. 



Side by side, therefore, structures typical of the opposite sexes are 

 built up, and an intersex, or what has been termed a mosaic gynandro- 

 morph, will result. Clearly, however, there must be a majority of cases 

 of cell division in which, as far as the sex chromosomes are involved, no 

 dislocation occurs. Therefore, since, as was stated before, the insects 

 are fundamentally females, they should remain so. And that such 

 was the experimental outcome our examination of the sexual organs 

 demonstrated. 



Granting that this is so, since disjunction can occur at any point in 

 segmentation, we have scope for every transition form between creatures 

 almost wholly female and those displaying a mosaic of equal portions of 

 both sexes, the latter as a result of mitotic dislocation in some early 

 cleavage stage, and the former generated by later occurrences of the 

 same nature. 



It has been advanced by Standfuss and others that these intersexes 

 in the Saturniidae and other families, are produced by the mere 

 presence of three sex determiners in one zygote. Without dislocation 

 this is impossible, for then the insects, whatever they might be sexually, 

 would be uniform in structure and this we have seen is not the case. 

 Such suggestions would not have been brought forward had dissections 

 been made, and the actual condition of the intersexes been deter- 

 mined. 



Besides, the direct cytological evidence of Bridges, who was fortunate 

 enough to come into possession of a stock of Drosophila rejoicing in 

 three sex chromosomes, showed that in such cases, exactly as I have 

 postulated, there was a preferential and uniform setting up of one sex 

 only. Only when, as in Morgan's experiments, dislocation occurred did 

 mosaics result. 



Description of the Genitalia of one of the P. pomonaria x P. lapponaria 

 Intersexes. Text-fig. 10. 



In this insect, as must naturally occur from its origin, the femaleness 

 is predominant. We see a fully developed ovipositor the right lobe of 

 which is perfect in every respect whilst the left is replaced by an uncus 



3—2 



