782 



SCIENCE 



[N. S. Vol. XXXIII. No. 855 



generations. Darkness is recessive to the 

 normal yellow and is not sex limited. Our 

 dark mutation is possibly identical with Mor- 

 gan's " melanotic " mutant. 



On the seventh of March we began to repeat 

 this experiment with the necessary control at 

 room temperature. On April 10, we found in 

 the first filial generation of the control cul- 

 ture kept at normal temperature a dark speci- 

 men. None of eleven new cultures kept in 

 the thermostat have thus far given rise to a 

 dark or any other type of mutant. Since 

 then dark individuals were found in another 

 control culture. 



From these experiments we must draw the 

 conclusion that a constant temperature of 

 30.5° does not necessarily produce mutations 

 in Drosophila, and second, that a dark form 

 of Drosophila may arise " spontaneously," 

 that means by forces at present unknown. 



2. Experiments with Radium. — A very large 

 number of experiments with radium were 

 undertaken, because it happened that the first 

 culture which we treated with radium chanced 

 to give us mutants. We succeeded in pro- 

 ducing short-winged specimens in two dif- 

 ferent cultures by treating them with radium ; 

 while thus far we have not yet observed this 

 mutation in cultures not treated with radium. 

 The manner of appearance of this short- 

 winged mutation was in both cases the same. 

 In the second filial generation of the flies 

 treated with radium, one or more short-winged 

 males appeared. The various forms of mating 

 were tried and yielded the result that the 

 short-winged condition is a sex-limited char- 

 acter. The wild normal males were found to 

 be heterozygous in regard to short wingedness. 

 Thus our short-winged mutant behaved like, 

 and is probably identical with the " minia- 

 ture "-winged mutant discovered by Morgan. 

 We have now bred the short-winged males and 

 females for five generations and find that they 

 remain constant. 



We expected that we might succeed in pro- 

 ducing short-winged mutants at desire, but in 

 this we failed. Although we treated more 

 than two hundred different cultures with ra- 

 dium we only observed the appearance of the 



short-winged mutation in the two cultures, 

 although we repeated the conditions of our 

 successful experiments quite frequently. In 

 both successful cases we submitted the ani- 

 mals only for one or two hours to the action 

 of radium. In one of the two cases the newly- 

 hatched imago alone, males and females were 

 treated for two hours with a weak radium, 

 preparation (10,000 units) which was coated 

 with collodium. It is possible that the alpha 

 rays may have affected the animals. In the 

 second successful case a strong radium bro- 

 mide preparation (over 1,000,000 units) in a 

 glass tube was applied for one hour to a mix- 

 ture of imago, eggs and young larvae. 



In five different cultures of flies treated with 

 radium the dark mutation appeared, but, while 

 the short-winged mutants appeared in both 

 cases in the second filial generation, there was 

 no regularity in regard to the appearance of 

 the dark mutants. 



In one culture treated with radium a white- 

 eyed female appeared in the first filial genera- 

 tion; it is possible that the existence of a 

 white-eyed male in a previous generation may 

 have escaped our notice. In two radium cul- 

 tures we observed the pink-eyed mutants, but 

 this was also found in cultures not treated 

 with radium. 



3. Experiments with Rontgen Rays have 

 given us thus far no mutants. 



Our results can be summarized as follows : 



1. A large number of cultures of Drosophila 

 were treated with high and constant tempera- 

 ture, with radium, and with Eontgen rays. 

 Four types of mutations were observed; a 

 dark form (which was the most common), a 

 pink-eyed, white-eyed and short-winged form. 



2. In the control cultures, which had not 

 been treated, the dark and the pink-eyed mu- 

 tations were also observed. As far as the 

 white-eyed mutation is concerned, it is prob- 

 able that it originated before the treatment 

 of the culture with radium. 



3. The short-winged mutants have appeared 

 thus far only in the cultures treated with 

 radium, namely in two cultures out of several 

 hundred. We did not succeed in producing 

 the short-winged mutation at desire by treat- 



