676 THE PHYSIOLOGY OF REPRODUCTION 



The results are represented in the following scheme, where R 

 represents the red-eyed factor and w the white-eyed : — 



(1) RR $ X WW (J gave Rw $ and Rtt? ?. 



(red) (white) (red) (red) 



(2) Rw '^ X Rw $ gave Rmj (J, ww $, Rw ?, and RR $. 



(red) (red) (red) (white) (red) (red) 



(3) Rio 5 X WW $ gave Rw <?, ioi« c?> R'W ?> and ww ?. 



(red) (white) (red) (white) (red) (white) 



(4) WW 9 X Rw $ gave ww $ arid Rw 5 • 

 (white) (red) (white) (red) 



(5) WW $ X WW $ gave wmj $ and i«zo $ . 

 (white) (white) (white) (white) 



These results are to be explained on the assumption that the 

 red-eyed male produces two sorts of spermatozoa, male-producing 

 and female-producing; and that whereas the female - producing 

 spermatozoa carry the factor for red eyes, the male-producing ones 

 do not. This conclusion has received cytological confirmation in the 

 discovery of Miss Stevens ^ that the male DrosopMla has a pair of 

 unequal chromosomes, and Morgan naturally assumes that the larger 

 or X chromosome carries the sex-linked characters. 



Doncaster had previously found in the currant moth. Abraxas 

 grossidariata, a condition of things which is the precise converse of 

 what Morgan has established for DrosopMla. He showed that in 

 with this insect there is a rare variety, which generally occurs only 

 in the female sex. This variety, which is called A. grossidariata 

 lacticolor, is a Mendelian recessive, so that when crossed with an 

 •ordinary grossulariata male, the offspring are all typical, the lacticolor 

 variety disappearing. Experimental crossings yielded the following 

 results : — 



(1) Lact. 9 X gross. ^ gave males and females all gross. 



(2) Heterozygous 9 x heterozygous ^ gave gross. <?, gross, ^, 



and lact. $. 



(3) Lact. 5 >< heterozygous <? gave all four possible forms 



(gross. (J, lact. ^, gross. ?, and lact. 5), the lacticolor males 

 being the first ever seen. 



(4) Heterozygous $ x lact. ^ gave gross. ^ and lact. 5. 



(5) Lact. ? X lact. ^ gave lact. ^ and lact. ? . 



(6) Wild gross. ? x lact. c? gave gross. (J and lact. ?. 



It is shown, therefore, that males of the lacticolor variety can be 

 produced by mating lacticolor females with heterozygous males (i.e. 

 with males obtained by crossing the two original varieties, and so 

 presumably bearing two sorts of gametes), but that the converse 



^ Stevens, "A Study of the Germ Cells of Certain Diptera,'' Jour. Exp. Zool., 

 vol. v., 1908. 



