Sammelreferat. 



191 



out completely a very perfect case in Drosoplüla. In this fly both sexes 

 normally have red ej'es. A white-eyed male appeared in his stock, which, 

 mated with a re i-eyed female, gave offspring of both sexes red-eyed. (Three 

 exceptional white-eyed males appeared among 1237 red-eyed offspring.) The 

 red-eyed heterozygotes mated with each other gave red-eyed females (24')g), 

 red-eyed males (ion), and white-eyed males (782). Heterozygous red-eyed 

 female x white-eyed male gave led and white eyes in both sexes; the white- 

 eyed females so produced paired with white-eyed males gave only white 

 eyes in both sexes, confirming the conclusion that the white eye is recessive 

 to red; and finally the white-eyed females mated with either crossed or 

 pure-bred red-eyed males gave all females red-eyed, all males white-eyed. 

 In the second paper Morgan shows that a short-winged form which 

 appeared, like the white eye, first in a male, behaves quite similarly in 

 inheritance to the white eye. 



In the Fowls studied by Pearl and Surface (and also by Goodale 

 and Spillmann, to whom they make reference), it appeared that the 

 female of the breed bearing the dominant character is ]iermanently hetero- 

 zygous in respect of the 'factor' for barring and also in respect of that for 

 femaleness. In Drosophila precisely similar evidence shows that the male 

 is heterozygous for the dominant characters red eye and long wing, and 

 also for the 'factor' which determines maleness, for the dominant character 

 is transmitted from the male only to his female offspring. Morgan makes 

 the following suggestion to account for these facts. He supposes that in 

 both cases all gametes bear a factor for maleness m, that femaleness is 

 produced by the superposition upon this of a factor F, but that two 

 different conditions occur in ditlcren cases. In cases like the Barred Fowl 

 and Abraxas, where the female is heterozygous for the dominant character 

 and for sex, the female has the constitution Ffmm, producing eggs Fm 

 and fm (f representing absence of F); the male in this case has the con- 

 stitution Ifram. producing spermatozoa fm. In Drosophila on the other 

 hand the female has tlie constitution FFmm, jiroducing eggs Fm; the male 

 Ffmm producing spermatozoa Fm, fm. The rlominant red-eyed character 

 IS intimately associated with F, so that the Fm spermatozoa which deter- 

 mine female offspring bear the red-eyed 'factor" the fm spermatozoa the 

 white eye. There are thus two chief differences between the two cases. 

 Firstly, in the Fowls etc. one F is ])resent in the female zygote, so causing 

 the existence of two kinds of eggs, Fm and fm, and F is altogether absent 

 in the male; while in Drosophila the female is homozygous for F, producing 

 only Fm eggs, and the male is heterozygous for F, so producing two kinds 

 of spermatozoa, Fm and fm. Secondly, in the first case the factor F must 

 be supposed to repel the dominant somatic character (barring etc) in game- 

 togenesis, while in the second it is coupled wiih it. Morgan appears to 

 reject the idea of repulsion, but it seems necessary to assume it in the 

 first case, unless one can imagine a present (dominant) character to be 

 coupled with the absence of a character, e. g. the factor for barring to 

 be coupled with f in the above scheme. Morgan's general scheme receives 

 some support from the fact that in Drosophila (Stevens) and in Man 

 (Guy er) the male is heterozygous in respect of the 'sex-chromosomes', 

 while the female is homozygous, whereas in Abraxas and other Lcpidoptcra 

 (Stevens, Cook, Doncaster) no such heterozygous condition of the male 

 has been found. But according to Guyer the Fowl has sex-chromosomes 

 of the same type as those in Drosophila and Man, a fact which is opposed 

 to Morgan's interjaretation, unless different breeds of fowls differ in this 



