INHERITANCE OF ABNORMAL VENATION. 11 



HISTORY OF THE PEDIGREED STRAIN. 



Before taking up the data concerning inheritance, it will be well to out- 

 line briefly the history of the chief pedigreed strains. Further details 

 are given in table 36. Mating 211 was the first family in these lines of 

 which a large number of offspring were described. Both parents were 

 abnormal in both wings . The wings of 177 offspring of this mating were 

 sketched. It was found that 31 per cent of the males were abnormal 

 and 65 per cent of the females. Successive generations after this, 

 breeding brother with sister, gave the following results: Abnormal 

 female by normal male (mating 257), 70 per cent of each sex abnor- 

 mal; abnormal female by abnormal male (mating 284), 62 per cent of 

 the males and 96 per cent of the females abnormal; abnormal female 

 by normal male (mating 330), 96 per cent of the males and 91 per 

 cent of the females abnormal; abnormal female by normal male (mat- 

 ing 367) , 64 per cent of the males and 91 per cent of the females abnor- 

 mal. A number of matings were made from the offspring of No. 367. 

 Matings 405 and 408 are of especial interest. 



In both of these matings both parents were abnormal in both wings. 

 Unfortunately there were a small number of offspring from each (25 

 and 29, respectively) , but all of the offspring of mating 405 were normal 

 and all those of mating 408 were abnormal. Three matings were made 

 from the offspring of 405. Of the 385 offspring of these, not a single 

 one showed the slightest trace of an abnormality, while of the 51 

 offspring of mating 440 (the parents being children of 408) only one, a 

 male, was free from abnormal venation. Mating 405, then, became the 

 starting-point of the "normal strain" and mating 408 the starting-point 

 of the "abnormal strain." 



As can be seen from table 36, the various generations of the abnormal 

 strain gave approximately, sometimes actually, 100 per cent abnormal 

 flies, although normal individuals were far from rare. Furthermore, 

 the intensity of the abnormalities increased. The greatest abnormality 

 noticed before the fifth generation is shown in fig. 20. Up to that time 

 all abnormalities were confined to the second longitudinal vein. Begin- 

 ning with the sixth generation, abnormalities appeared on the third 

 longitudinal vein. They became frequent by the tenth generation. In 

 the fifteenth generation they were common and abnormalities began to 

 be noticed on the fourth longitudinal vein. These have, even yet, rarely 

 exceeded small spurs near the distal end. About this time the fifth 

 longitudinal vein also began to be affected, and specimens such as are 

 illustrated in figs. 30 and 32 were found. Meanwhile increasingly great 

 abnormalities on the second and third longitudinal veins occurred. (See 

 figs. 37 to 42 for examples. The condition shown in fig. 43 is unique.) 



Turning now to the normal strain, three points should be borne in mind: 

 the parents in each generation were normal, it came from the same 



