386 H. G. MAY. 



The VBa stock in March revealed no such specimens, but the 

 Ba stock in June contained several of each. In that case they 

 were probably due to the appearance of a heterozygous female 

 in the previous generation. One of the stock bottles received 

 from Professor Zeleny contained a mixture of bar-eyed, full- 

 eyed and heterozygous individuals. These may have been due 

 to the appearance of a full-eyed male or a heterozygous female 

 at some previous time. 



The eyes of the males could not be distinguished from those of 

 normal wild flies. The facet numbers indicated in the table 

 are mere estimates obtained by counting a row of facets to the 

 middle of the eye and using the number obtained as a radius for 

 computing the number on the entire area. The eyes of wild 

 flies treated in the same way gave similar results. The eye of a 

 wild male which could be counted without turning was found 

 to contain 700 facets. 



The eyes of the heterozygous females had the characteristic 

 appearance of the eyes of such females obtained from crosses 

 between wild and bar-eyed flies and contained the corresponding 

 facet numbers. The ordinary bar eye has the shape of a crescent 

 with a notch near the middle of the concave side almost separating 

 the two ends of the crescent. One end is usually considerably 

 larger than the other and frequently contains the irregular facets 

 mentioned before. The eye of the heterozygous female has the 

 shape of the bar eye, but is much larger and does not contain 

 the irregular facets. As shown in the table, the heterozygous 

 females from the long-winged race had considerably larger eyes 

 than those from the vestigial-winged race. This is explained 

 by the fact that the average facet number in the bar eye of the 

 long-winged race is much larger than that of the vestigial- 

 winged race. 



Wherever possible the full-eyed males and heterozygous fe- 

 males that appeared were mated, but, with the exception of the 

 first case, no attempt was made to get a large number of off- 

 spring or to count the facets in the bar-eyed and heterozygous 

 offspring. Two of the individuals died soon after hatching and 

 the last two could not be mated because the experiments had 

 to be brought to a close. Of those mated one proved to be 



