Nos. 022-623] ORGAXIC EVOLUTION 



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mutations in Drosophila melanogaster Meig. 3 In both 

 species "confluent," a modification of the wing venation, 

 is similar in form, dominant over "normal" and 

 "lethal," when the fly is homozygous for the character. 

 The characters "yellow" and "forked" are sex linked 

 in both speck's and otherwise alike so far as the evidence 

 exists. Inasmuch as the earliest representative of Droso- 

 phila thus far known is a species not decidedly different 

 from those now existing as noted by Low (1850), who de- 

 scribed it from the amber of the Baltic Sea, and belongs 

 to the Lower Oligocene of the Tertiary Period, with an 

 age of from two millions to three millions of years, one 

 must infer that the genes common to the two species men- 

 tioned have been preformed for a long period of time, 

 and that nature has paid little attention to such muta- 

 tional changes as occur in connection with multiple allelo- 

 morphs. 



There are certain investigations widely separated as 

 to tlu-ir content, but apparently closely correlated as to 

 the underlying explanatory principles involved, which 

 must not be overlooked in a consideration of the changes 

 which may take place in hereditary units. These are 

 concerned with the differences involved in metabolism. 4 



On the one hand there are studies dealing with the di- 

 rect effects of a changed metabolism on the developing 

 individual. Here may be mentioned the work of Lillie in 

 connection with the "free-martin" of cattle; Steinach on 

 the transplantation of the gonads in rats and guinea- 

 pigs; Goodale on the grafting of ovaries in male fowls; 

 Pearl and Surface on the degeneration of the ovary in 

 cattle ; Riddle with pigeons, etc. On the other hand, there 

 are studies dealing with the indirect effects on inheri- 



