604 CALVIN B. BRIDGES 



somes should result. In mj^ experiments I have seen nothing 

 to correspond to the last case, and do not know what to look 

 for, on the dubious assumption that such a fly could live. The 

 three chromosomal form, I believe, would be a female on the 

 assumption that two sex chromosomes bearing the sex differen- 

 tiator produce a female, and that the extra chromosome would 

 not change this result. If we suppose that the result is a female, 

 what characters will she show? A two-X egg from an eosin 

 female fertilized by a red male would have two eosin factors and 

 the dominant red allelomorph. It seems likely that this female 

 would be red, perhaps diluted somewhat. I have never been 

 able to discover any eye color differences in the large class of 

 red females. Several taken at random, were tested individually 

 with wild males. If one of these females were three chromo- 

 somal I expected that there would be two eosin to one red male, 

 and that there would be a preponderance of females, in the ratio 

 of about two females to one male instead of the normal 1 : 1 

 ratio. The thirty cases tested gave, however, only the regular 

 proportion, 2 red 9 : 1 red cf : 1 eosin cf Using another and 

 better test, I am about to renew the search for these three-X 

 females. 



Although, in Drosophila, there is as yet no direct cytological 

 evidence concerning non-disjunction of chromosomes, in other 

 forms, there is cytological evidence in harmony with what the 

 genetic evidence demands in the present case. The work of Prof. 

 E. B. Wilson ('09) on Metapodius furnishes two such instances. 

 Here the number and size of the chromosomes in each individual 

 is constant, but this number ranges from 21 to 28, the variation 

 being due to loss of a F-chromosome from the typical 22-chromo- 

 some form to give the 21 form, and the addition of one to six 

 supernumerary F-chromosomes to give the higher groups. In 

 the 22-chromosome form, Wilson observed a few second sper- 

 matocyte divisions where both X and F passed to the same pole. 

 The result would be spermatozoa containing respectively twelve 

 and ten chromosomes. Wilson has shown that if these sperma- 

 tozoa are functional, the whole series of variations follows. The 

 production of spermatozoa with two or with no idiochromosomes 



