DEPARTMENT OF EXPERIMENTAL EVOLUTION. 123 



extensive one, which would require years for its completion, owing to 

 the great number and wide geographic distribution of the species. 

 As a contribution to this topic. Dr. Metz has sent to press a paper 

 which includes descriptions of 12 distinct types of chromosome groups, 

 distributed in about 30 species that have been studied. 



GENETICAL STUDIES ON TWO SPECIES OF DROSOPHILA. 



Dr. Metz has selected two species of Drosophila that have different 

 chromosome groups from D. ampelophila for comparison of genetical 

 behavior in the three. He has secured at least 16 mutations in these 

 two species within the last 12 months. In the species (as yet unnamed) 

 upon which most time has been spent 14 or more mutants have appeared 

 and are now being studied, and some very significant facts have already 

 appeared, even though some of the most interesting features still remain 

 to be investigated. 



"First and foremost appears the fact that some of the mutants in this 

 species are almost exact replicas of some in Drosophila ampelophila (studied 

 by Morgan, etal.), although the two species are in many ways very different. 

 Not only this, but in so far as they have been studied these characters fall into 

 similar groups on the basis of linkage. The most definite evidence of this 

 kind is shown by the sex-linked characters (which have been studied more 

 fully than the others). Two characters, "yellow" body-color and "forked" 

 bristles, are, so far as their characteristics show, almost exact duplicates of the 

 same (named) mutants in ampelophila, and a third character, "magenta" 

 eye, may perhaps bear a similar relation to that called "garnet " in ampelophila. 

 In both species these three characters are sex-linked. Furthermore, it seems 

 probable from evidence now being obtained that they show similar linkage 

 relations to one another in both cases. The evidence is not yet complete, but 

 it suggests that the factors compose a similar linear series in each species. 

 This, if it proves to be the case, can only be considered as indicating that 

 these two species possess a similar germinal organization, and that the 

 organization is a permanent feature; that is, a genetic continuity of germinal 

 structure, in so far as the factors are concerned, will be shown to exist in the 

 Drosophilas. If the sex-linked factors are located in the sex-chromosome 

 (X-chromosome) , as seems altogether probable, then this would mean that 

 the sex-chromosomes in these flies are genetically continuous; that they must 

 be transmitted essentially unchanged from one generation to another and 

 from one species to another in the course of evolution. 



"A brief review of these results has been pubhshed in Science, and a more 

 detailed report is in press in Genetics. 



"Further work with this new species and with the others I am studying 

 offers a most promising field for further investigations. It remains to be seen 

 whether the number of linkage groups in these will correspond to the chromo- 

 some number, as in ampelophila, and whether the euchromosomes can be 

 related to those in amelophila as can the sex-chromosomes. Since the number 

 and size relations of the chromosomes are different in each of the three species, 

 some very interesting questions are involved. Likewise, it will be of impor- 

 tance to learn whether or not the two sexes differ in respect to " crossing-over" 

 in my two species as they do in ampelophila, and whether this is correlated 

 with observable cytological evidence. In fact, a wealth of promising lines 



