No. 579] SHORTER ARTICLES AND DISCUSSION 



180 



effect of ether ; 3 a conclusion made even more certain by the fact 

 that other species were bred during the same time, under iden- 

 tical conditions, and with the same treatment, but without the 

 production of mutations. There is every reason to believe, 

 therefore, that the cause of the mutation in each case was purely 

 fortuitous. 



One of the aims of our work on the Drosophilas is to apply 

 the chromosome hypothesis to species having chromosomes dif- 

 ferent from those of D. ampelophila. The experimental work of 

 Morgan and others on D. ampelophila has pointed directly to the 

 conclusion that the four groups of linked factors which they have 

 studied are located, respectively, in the four pairs of chromo- 

 somes of this species. One of us has recently shown in the paper 

 above cited that several other species of Drosophila have chromo- 

 some groups differing from that of ampelophila in the number 

 and relative sizes of the chromosomes. Of the two species con- 

 sidered in the present paper, one, "species B," has six pairs of 

 chromosomes, and should therefore, on the chromosome 

 hypothesis, give six series of linked characters. The other, D. 

 tripunctata, has four pairs of chromosomes, but of a type 

 essentially different from that of ampelophila, and consequently 

 should also give essentially different linkage series. 



It is significant that both of the mutations which we have 

 found (axillary and confluent), are represented by similar muta- 

 tions in D. ampelophila. Judging from these it is not too much 

 to expect that among other mutations which may subsequently 

 arise in our species, some will likewise correspond to some of 

 those in ampelophila, and that upon this basis it may be possible 

 to homologize linkage groups, and thus more definitely homolo- 

 gize chromosomes in different species. 



C. "W. Metz and B. S. Metz 



A SEX-LINKED CHARACTER IN DROSOPHILA 

 REPLETA 



Drosophila repleta Wollaston (D. punctulata Loew) is a 

 cosmopolitan species, though only recently introduced into the 



the appearance of mutations in Drosophila ampelophila. Cf. Amee. Nat., 

 1914, "The Failure of Ether to Produce Mutations in Drosophila." 



