702 THE AMERICAN NATURALIST [Vol. LI 



number. The number of chocolate males, especially, falls low. 

 The totals seem to indicate that this low number of chocolate 

 males in comparison to the number of normal males is partially 

 due to the fact that some of the chocolate males have been 

 called normal, for in practically all of the matings, the number 

 of normal males exceeds the number of normal females. This 

 is unusual, for the writer has examined large numbers of wild 

 DrosopJiila huscJcii and in a large majority of the cases the num- 

 ber of females has been equal to or greater than the number of 

 males. So it may be that the males approximate the normal 

 color more rapidly than the females and since the flies were ex- 

 amined only once a day, some of the chocolate males were mis- 

 taken for normals. Some counts were made, examining the flies 

 twice a day, to test this supposition and they indicated that 

 better ratios could be obtained in this manner. But since the 

 work was completed before this was realized, the difference to 

 be obtained by twice-a-day counts was not thought to be of 

 sufiScient importance to require the repetition of the experi- 

 ments. Also in these matings, the relative number of chocolates 

 was lower where mass cultures were made. The ratio for all of 

 the F2 flies examined was 4.21 normals to 1 chocolate. 



The Genetic Behavior of Red and Chocolate when they are 



MATED together 



Red males were crossed to chocolate females and red females 

 to chocolate males and in the of each cross nothing but normal 

 flies appeared. The results of the of these crosses are given 

 in Table III. 



Here again the number of normal males is considerably above 

 the number of normal females. This could be explained as 

 before, that some of the chocolate males have been mistaken for 

 normals, thus increasing the normal class and decreasing the 

 chocolate class. Since the number in the classes of red and 

 chocolate each fell low in their respective crosses to wild, we can 

 expect the number in these classes to be low in this cross. Ta- 

 king this fact into consideration, the ratio can be considered a 

 1:2:1 ratio and gives indication of linkage between the two 

 characters. No red-chocolate double recessives were found, 

 therefore the two mutations may be interpretated as being 

 located in the same chromosome. 



