236 THE AMERICAN NATURALIST [Vol. LVI 



tions of the three genes on the chromosome map re- 

 semble those in melanog aster. Yellow is about three 

 units from the end instead of at the end; singed is at 

 about 35 instead of 21 and forked is at about 58 instead 

 of 56.5. 



The evidence is not sufficient to warrant the conclusion 

 that these are actually homologous series, but the fact 

 that such series exist suggests that by the present means 

 it may eventually be possible to obtain reliable data for a 

 comparison of the chromosomal make-up of the different 

 species. 



Among the other characters in ivillistoni which show 

 some resemblance to characters in melanog aster or sim- 

 idans the following may be noted as a matter of record, 

 although there is little indication of their being actual 

 parallels : orange and peach (which look alike) resemble 

 coral or ruby; beaded is similar to the cut allelomorphs 

 both morphologically and in respect to its sterile fe- 

 males and poorly viable males; triple suggests bifid, and 

 morula looks like lozenge. The small bristle of nnllistoni 

 may be comparable to the tiny bristle-2 of simulans. 



The fact that the X-chromosomes in willistoni are mor- 

 phologically like the large autosomes and not like the 

 X-chromosomes of m.elanogaster suggests that we ought 

 to compare, not only the sex-linked groups of the two 

 species, but also the sex-linked group of willistoni with 

 the non-sex-linked groups of melanogaster. This has 

 been done, but without revealing any significant indica- 

 tion of parallelism. 



In conclusion it may be noted that although the evi- 

 dence is not yet clear on the genetic relationship of the 

 sex chromosomes in melanogaster and willistoni, yet if 

 the above suggestion is correct, that the X-chromosome 

 of melanogaster corresponds to part of the X-chromo- 

 some in willistoni, then the resemblance between the 

 chromosome groups of the two species is only super- 

 ficial. It may also be noted that the genetic ''map" of 



