732 THE AMERICAN NATURALIST [Vol. XLVIII 



characteristics. Tables XII to XX give the results in 

 systematic form. 



TABLE XII 



F, Counts of the Cross Beaded $ X Curved 



One of the most striking characteristics of these second 

 chromosome crosses is that the F 1 flies fall into two 

 classes or possibly into three classes with reference to the 

 offspring that they produce. These classes I have called 

 Type 1, Type 2, and Type 3. 



In Type 1 there is no linkage between Beaded wings 

 and the second chromosome character, but Beaded- 

 winged flies occur with equal frequency in all classes of 



TABLE XIII 

 P, Counts of the Cross Beaded $ X Arc <J 



offspring. In Type 2 there is linkage of Beaded wings 

 with the second chromosome characters, so that the 

 Beaded wings appear more frequently in flies showing 

 the characters of the Beaded parent. In Type 3, which 

 occurs only a very few times and is not very marked 

 except in Table XX, Beaded wings appear to a greater 

 percentage in the offspring whose other characters are 

 not those of the Beaded parent. (/. e., " repulsion" occurs 

 between the factor for Beadedness and that for the 

 second chromosome character with which it entered the 

 cross.) I do not wish to emphasize Type 3, but concern- 

 ing the other two it is important to note that about one 

 half of the Fj flies seem to be of Type 1 and one half of 

 Type 2. 



In Type 2 in the cases here adduced the linkage is 



