No. 585] SHORTER ARTICLES AND DISCUSSION 



5S1 



of material between the two chromosomes as indicated by the 

 crossed lines, then males arise with a different arrangement of 

 the characters from that which had appeared in the grand- 

 parents. 



In the diagram v, f and Br stand for vermilion eye, furrowed 

 eye, and bar eye, respectively; while V, F and br stand for 

 the normal allelomorphs of these characters, i. e,. red eye, not 

 furrowed and not bar. Reading from the left the top dotted 

 line includes v, F and br. but since F and br are normal the flies 

 will differ from norma] forms in the one character alone, viz., 

 vermilion. The dotted line below includes V, f and Br, hence 

 the males receiving this chromosome are furrowed bar. Re- 

 ferring to the table showing the cross between a vermilion bar 

 female with a furrowed male we see that there were 28 vermilion 

 and 15 furrowed bar flies. Reading from the left again and 

 omitting the normal allelomorphs, the upper dash line includes 

 vermilion and furrowed and the lower dash line includes bar 

 alone. The table shows that there were only three vermilion 

 furrowed and six bar males, hence the interchange of material 

 between vermilion and furrowed took place less frequently 

 than it did between furrowed and bar. Since the per cent, 

 of crossing over between any two genes is taken as the index of 

 the relative distance between those genes, then furrowed lies 



representatives were found in this cross. 



Summary and Conclusions 

 Crosses were made with mutant stocks of Drosophila with 

 wild stock from many localities in the United States, from the 

 West Indies, France and Australia in order to discover, if pos- 

 sible, if hybridization is an essential factor in the formation of 

 mutant races. From 16.637 flies of the F 2 generation seven 

 flies arose which varied from the normal type and which bred 

 true. If we discard the four with the character "tau " for 

 reasons given above, then the result is narrowed to three flies 

 with two characters. This gives one mutant to every 5,545 flies. 

 Therefore, a mutation has occurred so seldom that we can 

 scarcely attribute hybridization as its cause. It is highly prob- 

 able that if the same number of wild flies had been reared under 



