MISCELLANEA 199 



Sex Limitation in tlie Inheritance of Eye-Colour in Flies* 



Drosopkila is a fly of common occurrence during the Summer. 

 It deposits its eggs in fruit and various culinary plants. The 

 eyes of the wild fly are dull red. It has been shown experiment- 

 ally by Professor T. H. Morgan, of the Zoological Laboratory, 

 Columbia University, that the colour is due to a mixture 

 of three pigments, namely, red, pink, and orange. Flies 

 are known which, instead of having the dull-red colour 

 of the species, have either a vermilion, a pink, or orange colour. 

 The experimental e^ddence leads us to believe that these 

 colours are produced by the loss, from the germ-cells, of one 

 of the three factors which make up the dull red of the 

 species. Vermilion, for instance, is the colour which results 

 when the pink factor is lost ; in other words, it is the colour due 

 to the presence of the two factors producing red and orange. 

 Similarly, the pink eye is due to loss of red, and is the 

 colour manifested when only pink and orange are present. The 

 orange eye is due to the loss of both red and pink. 



It follows from this, that if a female fly with vermilion eyes 

 be crossed with a male having pink eyes, we should expect that 

 all the first generation would have the dull-red eyes of the species. 

 If these, then, be interbred, we should further expect that the 

 second generation Avould produce some flies with orange eyes, 

 together vnth some whose eyes ^vill be vermilion, some red, and 

 some pink. 



It is, however, an apparently strange fact, which has been 

 experimentally shown by Professor Morgan, that the first 

 generation consists not of flies all having red eyes, 

 but of two sex groups. Of these, all the males have 

 vermilion eyes and all the females red eyes. We are dealing 

 with a definite and obvious sex-limited character — that is to 

 say, that the character of sex is in some way definitely bound 

 up with the presence of another character. This character 

 is pinkness, for as we have seen, the vermilion colour is red minus 

 pink. In other words, the males of the first hybrid generation 

 whose eyes are all vermilion-coloured lack pinkness, while the 

 females all ha^'ing the red eyes therefore possess it. This is 

 an extremely interesting fact because it shows two things quite 

 incontestably. First, that qualities do not depend upon environ- 

 ment, because these flies are reared under the same external 

 conditions. Second, that sex may carry with it an association 

 with other qualities. 



In the case just described the vermilion-eyed female was 



* Further information of this complex subject will be found in the 

 " Journal of Experimental Zoologj." Vol. XI., 1911. 



