OF MUTANT CHARACTERS. 



207 



ment with the black speck value and with the short arc speck value 

 found. 



The coincidence corresponding to these data is 44.2, calculated as 

 follows : 



2625 X 28 X 100 

 (1038 + 28) X (128 + 28) " ^^'^ 



This coincidence, as compared with the coincidences found for the 

 other cases involving the region around black, purple, vestiguil, and 

 curved, were surprisingly low, and suggested that the coincidences 

 involving the right end were different from those involving the part 

 then regarded as the left end, but now regarded as the middle of the 

 chromosome. 



There is one other important linkage experiment involving arc, 

 namely, the black arc morula back-crosses with balanced inviabiUty. 

 These crosses, which furnished a total of 6,794 flies (table 84), are 

 treated under the section on morula. 



Table 54. — Pi, purple 9 X arc speck cf; B. C, Fi wild-type 9 X stock 



purple arc speck cf . 



Table 55. — Summary of all linkage data involving arc. 



