378 CARNEGIE INSTITUTION OF WASHINGTON. 



enable us to identify them as a distinct type; and the way in which the 

 sex-linked characters are distributed shows that they should possess 

 three X-chromosomes. A study of their germ-cells reveals three 

 X-chromosomes . 



Another unusual chromosome-group has been found by L. V. 

 Morgan in which the two X-chromosomes are attached to each other, 

 forming a single long V-shaped chromosome. These individuals are 

 females. When bred they show a reversal of the usual method of distri- 

 bution of the sex-linked characters. Thus a "double-yellow" female 

 bred to a wild-type male gives only yellow daughters and wild type sons. 

 In this strain descent is from mother to daughter and from father to son. 



In another strain, individuals were found that are intermediate 

 between males and females. The distribution of mutant characters 

 in families in which such ''intersexes" are present shows that the inter- 

 sexes should possess three members of the II-, III-, IV-chromosomes, 

 but two X-chromosomes. Among the sisters of the intersexes were 

 also found females that possessed the three members of each kind of 

 chromosome. These were triploid individuals. Such triploids con- 

 tinue to produce intersexes and triploids. Since the intersexes are 

 sterile, the stock can be continued only from triploids. The mature 

 eggs of triploid females are left with either two, or only one of each 

 chromosome, but the assortment of these chromosomes is not inde- 

 pendent, since there are more eggs having two X's and one of each of 

 the other chromosomes, or, vice versa, one X and two of each of the 

 autosomes, than would be expected from random assortment. From 

 some of the unusual chromosome combinations there are produced 

 triplo-X indi\'iduals, triplo-IV individuals, and individuals possessing 

 one X-chromosome, but three of each of the autosomes. All of these 

 types have been identified. The evidence shows that individuals 

 possessing an extra II- or an extra Ill-chromosome die, a result that 

 was previously indicated by the fact that non-disjunction of these 

 chromosomes was not met with and from a study of autosomal mosaics. 



The triploid flies are larger and coarser than normals and also have 

 large, rough eyes. Their eggs, as shown by genetic tests, contain all 

 possible combinations of chromosomes, behaving as though non- 

 disjunction takes place simultaneously in each set of three. Among 

 the offspring of a triploid female (mated to a normal male) there is one 

 class that has three II's, three Ill's, and three IV's, but has two X- 

 chromosomes. This individual is an intersex, more like a male than 

 like a female. There is another class that has three II's, three Ill's, 

 but only two I Vs. It also is an intersex, but more like a female. 



Thus sex itself in this animal is shown to be an expression of a balance 

 between the X-chromosomes and the autosomes. The results show 

 that the differentials that determine sex are not confined to the sex- 

 chromosomes alone. Some appear to be in the II- and Ill-chomo- 

 somes, and others in the IV-chromosome. 



