42 T. H. MORGAN 



DISCUSSION 



The color of the body of the wild fly appears from the 

 experimental data to be due to at least three factors viz., yel- 

 low, black, brown. It has been shown in a former paper that 

 the red eye of the wild fly is also due to the presence of three 

 factors viz., vermilion, pink, orange. In both series one at 

 least of the three factors is sex-linked; the factor for black in 

 the one and for pink in the other. In crossing both series give 

 almost parallel results. In the eye-color series the factor for 

 orange is always present, either simplex or duplex. In my 

 former paper I could not determine whether it is sex-linked 

 or not, because it had never dropped out, but since then I have 

 obtained a new mutation in which orange has dropped out, 

 and, by suitable experiments, it has been shown that this factor 

 also is sex-linked. It appears then that in the eye color series 

 there are two sex-linked factors, P and 0, and one not sex-linked, 

 V. In the present series brown occupies a similar position in 

 the symbolism used to that of the orange factor in the eye color 

 series, but on the basis of this similarity it would not be justi- 

 fiable to conclude that the brown factor is sex-linked. 



In this connection I may record that during the summer of 

 1910 there appeared for a time, in one of my cultures, flies 

 that had almost no color in the body although the eyes were 

 red. A few pigment granules brownish in color were scattered 

 over the abdomen. The flies resembled in some respects flies 

 that had just emerged from the pupa case. The flies were 

 extremely weak and died after a few days without progeny. 

 Whether they represent the loss of the brown factor, or of the 

 color producer can not be stated. Since they appeared in cul- 

 tures of gray flies the latter interpretation seems more probable. 



Whether the comparison drawn above between the eye color 

 series and the body color series has any real significance can, 

 of course, be only a matter of conjecture. It should be pointed 

 out that any eye color may be combined with any body color, 

 and I have been unable to detect any correlated effect of these 

 two combinations upon each other, except such effect as is due 

 to color contrast. 



