122 



SCIENCE 



[N. S. Vol. XXXII. No. 



RX — W (red male) 

 WX— WX (white female) 



RWXX (50^)— WWX (50;;;) 



The converse cross between a white-eyed 

 male EWX and a wild, red-eyed female shows 

 that the wild female is homozygous both for 

 X and for red eyes. Thus: 



WX— W (white male) 

 RX — RX (red female) 



RWXX (60;^)- RWX (50^) 



The results give, in fact, only red males and 

 females in equal numbers. 



General Conclusions 



The most important consideration from 

 these results is that in every point they fur- 

 nish the converse evidence from that given 

 by Abraxas as worked out by Punnett and 

 Eaynor. The two cases supplement each 

 other in every way, and it is significant to 

 note in this connection that in nature only 

 females of the sport Airaxas lacticolor occur, 

 while in Drosophila I have obtained only the 

 male sport. Significant, too, is the fact that 

 analysis of the result shows that the wild 

 female Abraxas grossulariata is heterozygous 

 for color and sex, while in Drosophila it is the 

 male that is heterozygous for these two char- 

 acters. 



Since the wild males (EWX) are hetero- 

 zygous for red eyes, and the female (EXEX) 

 homozygous, it seems probable that the sport 

 arose from a change in a single egg of such a 

 sort that instead of being EX (after reduc- 

 tion) the red factor dropped out, so that EX 

 became WX or simply OX. If this view is 

 correct it follows that the mutation took place 

 in the egg of a female from which a male was 

 produced by combination with the sperm 

 carrying no X, no E (or W in our formula). 

 In other words, if the formula for the eggs of 

 the normal female is EX — EX, then the for- 

 mula for the particular egg that sported will 

 be WX; i. e., one E dropped out of the egg 

 leaving it WX (or no E and one X), which 

 may be written OX. This egg we assume was 

 fertilized by a male-producing sperm. The 

 formula for the two classes of spermatozoa is 



EX — O. The latter, O, is the male-producing 

 sperm, which combining with the egg OX 

 (see above) gives OOX (or WWX), which is 

 the formula for the white-eyed male mutant. 

 The transfer of the new character (white 

 eyes) to the female (by crossing a white-eyed 

 male, OOX to a heterozygous female (FJ) 

 can therefore be expressed as follows: 



OX- 



RX- 



- ( white male ) 

 -OX (F, female) 



RXOX— RXO— OOXX— OOX 



Red Red White White 



female male female male 



It now becomes evident why we found it 

 necessary to assume a coupling of E and X 

 in one of the spermatozoa of the red-eyed F^ 

 hybrid (EXO). The fact is that this E and 

 X are combined, and have never existed apart. 



It has been assumed that the white-eyed 

 mutant arose by a male-producing sperm (O) 

 fertilizing an egg (OX) that had mutated. 

 It may be asked what would have been the 

 result if a female-producing sperm (EX) had 

 fertilized this egg (OX) ? Evidently a hetero- 

 zj'gous female EXOX would arise, which, fer- 

 tilized later by any normal male (EX — O) 

 would produce in the next generation pure 

 red females EEXX, red heterozygous females 

 EXOX, red males EXO, and white males 

 OOX (25 per cent.). As yet I have found no 

 evidence that white-eyed sports occur in such 

 numbers. Selective fertilization may be in- 

 volved in the answer to this question. 



T. H. Morgan 



Woods Hole, Mass., 

 July 7, 1910 



ELECTROLYTIC EXPERIMENTS SHO\^^NG INCREASE 



IN PERMEABILITY OF THE EGG TO IONS AT 



THE BEGINNING OF DEVELOPMENT 



It has been shown that at the beginning of 

 development of the egg there is an increase 

 in the absorption of oxygen (Warburg) and 

 excretion of carbon dioxide (Lyon). This is 

 evidently accompanied by increased oxidation 

 within the egg, but varying views as to the 

 cause of the increase have been advanced. 

 The more rapid oxidation might be due to the 



