200 THE SECOND-CHROMOSOME GROUP 



STRAP (V). 



(Plate 8, figures 1, 2, 3.) 



ORIGIN OF STRAP. 



The mutation "strap" was found by Morgan about April 1912, in 

 an experiment involving vestigial flies. The first individual (a female) 

 was regarded simply as a vestigial with extra long wings. The name 

 "strap" was given because of the extreme narrowness of the wings. 

 As in the case of vestigial, they extend laterally from the body, though 

 not quite as nearly at right angles as are the wings of vestigial. 



INHERITANCE OF STRAP. 



The first female was bred to a vestigial brother and produced in Fi 

 all vestigial offspring. In F2, however, the strap-winged type reap- 

 peared in about a quarter of the individuals, showing that strap was 

 not simply a "long" vestigial, but that there had been a distinct 

 mutation. That the mutation was not sex-linked was evident from 

 the Fi result, since the sons of the strap female had failed to show the 

 strap character. 



STOCK OF STRAP. 



Some of these Fo strap individuals were inbred and gave a stock 

 practically all of which were "strap." Selection was practiced for 

 many generations to increase the length and narrowness of the wings, 

 but WTithout success further than to establish a homogeneous stock, in 

 which every individual was typically strap. 



DESCRIPTION OF STRAP. 



While there is considerable variation in the character, the wing is 

 always found to be longer than vestigial. The tip of the wing is 

 narrow and elongated, while the base is broader than vestigial, espe- 

 cially on the inner (rear) margin, so that the whole wing often has a 

 "leg-o'-mutton" appearance. The venation is normal; that is, the 

 bases of all the longitudinal veins are present and usually nearly all 

 of the second longitudinal vein which runs out along the narrow tip 

 either near or at its outer (forward) margin. The rest of the venation is 

 cut away along with the blade of the wing The balancers are affected 

 in an analogous manner, the terminal segment being much reduced, 

 though probably never gone, as it often is in vestigial. A curious 

 correlation noted is that the more of the wing-blade there is present 

 the larger is this terminal segment of the balancer and also the closer 

 to normal is the position of the wing. _ , 



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