278 



SCIENCE 



[N. S. Vol. LIV. No. 1395 



the red-eyed character, were mated with white- 

 eyed males. Nineteen of these were used as 

 controls and sixteen were X-rayed soon after 

 emerging from the pupa and immediately 

 before mating. The rayed females were the 

 sisters of the controls. None of the nineteen 

 control pairs produced white-eiyed males. 

 One of the rayed females was sterile. Of the 

 fifteen fertile rayed females, twelve produced 

 one or more white-eyed males. The total 

 number of ofispring in the first generation 

 produced by the control pairs was 65Y9 

 (3367 d", 3312$) aU red-eyed, and by the pairs 

 in which the females were rayed it was 2460 

 (122Y red-eyed <S, 1211 red-eyed $, 20 white- 

 eyed <S and 2 gynandromorphs) . In the fourth 

 experiment seven wild-type sister females 

 were used, three were kept as controls and 

 four were rayed. All were mated with white- 

 eyed males. One of the control females pro- 

 duced one white-eyed male. Two of the three 

 rayed females produced white-eyed males, one 

 producing three and the other one. 



In the first and fourth experiments the 

 white-eyed males were also homozygous for the 

 character, " dumpy," which is located in the 

 second chromosome. Of the six white-eyed 

 males produced in these experiments five had 

 normal wings and the other died before its 

 wings expanded. 



Twenty-three out of the twenty-four ex- 

 ceptional white-eyed males came from eggs 

 which were laid during the first six days after 

 raying and mating. The other male came 

 from an egg probably laid on the seventh day 

 after raying. Further the exceptional white- 

 eyed males divide themselves into two groups 

 corresponding to eggs laid during the earlier 

 part and the later part of this six day period. 



That the presence of these white-eyed males 

 could be due to natural non-disjunction and 

 not to any effect of the X-rays seems extreme- 

 ly unlikely from the following considerations: 

 In ex]3eriment 71, out of 7 fertile sisters the 

 two which were X-rayed produced white-eyed 

 males. The chance in a random picking of 

 getting a particular two out of seven can be 

 shown to be 1 in 42. "We may add the results 

 of experiments 76 and 77 since the females 



used in these experiments were all the off- 

 spring taken at random of two pairs. If the 

 result here was not due to X-rays, then in tak- 

 ing at random 12 females from 26 for raying 

 we must have taken the only 10 which pro- 

 duced white-eyed flies. The chance of doing 

 this can be shown to be 1 in 9,600,000 tries. 



Since the white-eyed males produced by the 

 X-rayed females when crossed to white-eyed 

 dumpy males were normal winged, the second 

 chromosome of the female can not have been 

 affected to the extent of the elimination of 

 the gene for normal wing. 



It may be stated that a repetition of these 

 experiments is in progress and that a number 

 of experiments have already been carried far 

 enough to confirm the earlier fimdings. 



In order to determine whether the whole 

 or a part of the X-chromosome is affected by 

 the X-rays, two strains with sex-linked charac- 

 ters have been used, both obtained through 

 the kindness of H. H. Plough — an eosin-minia- 

 ture stock and a scute-echinus-cut-vermilion- 

 garnet-forked stock. Males of both of these 

 stocks have been used in experiments similar 

 to those described. In all cases so far the ex- 

 ceptional males produced by the X-rayed fe- 

 males (the control females have produced no 

 exceptional males) have all the sex-linked 

 characters. 



Since the eggs which have produced the 

 exceptional white-eyed males were probably 

 rayed either 2 to 3 or 5 to 7 days before lay- 

 ing, there seems reason to believe that they 

 were acted on by the X-rays while preparing 

 for one of the maturation divisions. (Com- 

 pare here the work of H. H. Plough, 1917, 

 on the effect of temperature on crossing over.) 



We know from the work of Stevens^ and 

 Metz^ that the X-chromosomes of Drosophila 

 melanogasier {am.pelophila') behave, in the 

 male, differently from the other chromosomes 

 in the maturation divisions. If, as seems 

 probable, the chromosomes during division go 

 through a stage in which they are particularly 

 susceptible to X-rays, then it would seem 



- Stevens, Froc. VII. International Zool. Cong., 

 1907. 

 3 Metz, Journ. Exp. Zool., 1914. 



