536 



SCIENCE 



[N. S. Vol. XXXIII. No. 849 



female only pinks and whites were produced. 

 Evidently the change has taken place in the 

 white. If we express the ordinary red color 

 as the outcome of two factors C and E then 

 the ordinary whites will be OE while the new 

 white will be represented by 00. The tests 

 that I have made so far corroborate this view, 

 giving the combinations expected from the 

 formulse. Theoretically the new white should 

 behave towards the new pink as a sex-limited 

 character in the same way in which the origi- 

 nal white behaved towards the reds, and such, 

 in fact, is the case. Moreover, it is clear why 

 in the one case (white and pink) there should 

 be sex-limited inheritance and in the other 

 (red and pink) a diilerent kind of inheritance, 

 provided, as the facts strongly indicate, that 

 the factor for pink is contained in another 

 part of the hereditary mechanism than the 

 factor for white. In other words, the factor 

 for white (absence of red) is connected with 

 the factor that determines sex, while that for 

 pink is contained in a different part of the 

 cell. It is this evidence that has seemed to me 

 to show that the phenomenon of sex-limited 

 inheritance is due to an intimate physical 

 relation between the sex factors and the other 

 factors in question ; and the most obvious con- 

 nection is that the relation is to be found in 

 the chromosomes that carry both the sex factor 

 and those factors that are sex limited. 



The Bright Red Eye 



This color arose in hybrids produced by 

 breeding flies with miniature wings to wild 

 stock. A small percentage of the male off- 

 spring had bright red eyes. This cross has 

 been repeated a number of times and has 

 always given some bright red-eyed flies. There 

 can be little doubt that it is produced in some 

 way by the cross. I foimd, it is true, one in- 

 dividual with bright red eyes in the wild stock 

 from which the cross was made, but only once 

 in many hundreds of flies examined, while 

 the production of coral eyes is a constant 

 feature of the hybrids. 



The bright red eye is sex limited, as shovTn 

 by the fact that in certain combinations it has 

 appeared only in the males. When such males 



were bred to their red-eyed sisters, bright red- 

 eyed females as well as males were produced. 

 When two bright red-eyed individuals are 

 mated they produce only bright red-eyed off- 

 spring, and I have a large stock of these flies 

 that originated in this way. 



The bright red eye differs from the red eye 

 in being conspicuously more brilliap.t in color. 

 No intermediate condition has ieen found. 

 The relation between this color and red and 

 pink has not yet been fully worked out. 



The Orange Rye 

 A cross between a white-eyed male and a 

 red-eyed female (heterozygous for pink) pro- 

 duced flies with red, bright red, pink, white 

 eyes, and a few flies with eyes having a faint 

 orange tinge. The eyes are much lighter than 

 pink eyes, and do not seem to intergrade with 

 them. The appearance of the orange color in 

 this and in other cultures followed the ap- 

 pearance in them of the bright red eye, and 

 seems to be connected with the factor for 

 bright red. As yet this relation has not been 

 clearly worked out. Orange bred to orange 

 has given in some cultures stock that has pro- 

 duced many hundred flies with orange eyes 

 only. The orange eye has not been found to 

 be sex limited in any of the many combina- 

 tions that have so far been made. Thus while 

 white and bright red eye colors are sex limited 

 the other two colors, pink and orange, do not 

 show this form of inheritance. Now that pure 

 cultures of all the stocks have been obtained, 

 their interrelations will be further studied. 



The Spotted Eye 



On two or three occasions flies appeared in 

 which some of the ommatidia of the compound 

 eye were red and the rest white. The last in- 

 dividual of this kind that appeared was obvi- 

 ously a white fly with about one fourth of the 

 area of one eye red, the rest white. The 

 other eye was entirely white. Unfortunately 

 the fly died before she could be tested. The 

 occurrence of this mutation is of interest in 

 its bearing on the origin of the spotted condi- 

 tion in many of our domesticated animals. 



These cases are comparable to heterozy- 

 gous flies with one long wing and one short. 



