386 GENES MODIFYING NOTCH. 



especially on the right side, is male. The genitalia (not shown here) 

 are like those of the normal male. While, therefore, there is no such 

 sharp line of division as is found in many Drosophila mosaics and gynan- 

 dromorphs, yet the distinction between the characters in the different 

 regions is sharp. There is nothing in the hypothesis of chromosomal 

 elimination that requires that the critical division should occur so early 

 that the nuclei that go to one half of the egg are separated from those 

 that go to the other, or that even if it occurs at a very early division the 

 separation of the two groups of nuclei need be exactly medial. 



The critical evidence obtained in other Drosophila gynandro- 

 morphs proves that abnormality must have been due to chromosomal 

 elimination rather than to other processes, such as those suggested 

 earlier by Boveri (1883) and by myself (1905) to account for other 

 gynandromorphs. The critical evidence rests on the presence in the 

 two parents of a pair of genes in other than the sex chromosome. 

 The same analysis can not be used in a case of this kind where only 

 sex-linked characters are involved. 



An examination of this case from the point of view of the two 

 other hypotheses referred to above leads to the following analysis: 

 Boveri's view calls for belated fertilization, so that the entering sperm 

 unites with one only of the two first-division products of the egg- 

 nucleus. Now, in this case we know that the egg-nucleus contained 

 the genes for red-eyed and Notch, hence the products of such a 

 division also contained these genes. If then to one of them the sperm- 

 nucleus is added (bearing the eosin ruby genes) that half will give rise 

 to female parts having the dominant character (red eyes and Notch 

 wings), and the other first divisional product of the nucleus (haploid 

 with one X), while expected to produce male parts perhaps, yet such 

 male parts would have red eyes and Notch wings also. Clearly 

 Boveri's view will not fit this case. 



On my earlier view, gynandromorphs in insects may arise from super- 

 numerary fertilizations. In this case we must suppose that two 

 female producing sperms enter the egg, one fusing with the egg-nucleus 

 and give rise to the female parts, the other developing separately and 

 giving rise to the male parts, which would then have the eosin-ruby 

 eye-color and normal wings. My own hypothesis fits the present case, 

 but I think nevertheless that all such cases in Drosophila are more 

 probably due to elimination because where critical evidence has been 

 obtained it shows beyond doubt that the result was due to chromo- 

 somal elimination. 



