1916] Beeves: Inheritance of Extra Bristles in Drosophila 499 





TAB 



LE VII 













EXTEA 



X Extra 









milv — 



Bottle letter 



Number of 

 extra bristles 



N. 



ex. 



Per 



cent 



F3 Y 



e" 



c^2 



?3 



48 



6 



11.11 





B 





1 



70 



5 



6.6 





F 





1 



88 



7 



4.21 





g 





1 



18 



5 



21.8 





d^ 





1 



10 



4 



28.5 





d= 





1 



60 



15 



20.00 



F. X 



a 





2 



76 



10 



11.6 





f 





1 



47 



7 



7.84 





xc 





1 



40 



5 



11.11 





Xo 





1 



106 



15 



14.85 



F5 X5 



f. 





1 



50 



14 



28. 





c- 





1 



23 



6 



20.3 



These tables show that extra mated with extra gives a greater and 

 a steadier percentage of extra-bristled than when normals were 

 crossed with extras. 



The Effect of Environment 



1. The Influence of Food. — In seeking causes for the variability 

 in the number of extra bristles, observations were made on certain 

 environmental influences, food and temperature. 



It seemed to make no difference in the number of extra bristles 

 whether the food was moist or dry, as .practically the same number 

 of extra-bristled flies appeared under either set of conditions. Thus 

 the variation- differed from the abdominal variation described by 

 Morgan (1915), in which moist food was the controlling factor. 



As it is impossible to keep the bananas used for food at the same 

 degree of acidity, and as extras appeared in all cultures, the degree 

 of acidity can play no important part. 



The abundance of food, also, could not play an important part, 

 as the extra-bristled flies occurred most often in the middle of the 

 counts and continued to appear up until the end. The normals 

 occurring in inbred selected culture appeared all through the hatch- 

 ings but in larger numbers at first, thus differing from MacDowell's 

 (1915) result, who found that the extra-bristled flies appeared in 

 larger numbers in the first part of the hatching. 



Table VIII gives a few examples from the families studied. In 

 each case a pair of flies was placed in a bottle and then, before their 

 eggs began to hatch, they were removed to a second bottle, where a 

 new batch of eggs was laid. These hatchings are shown in table VIII. 



