SEXUAL DIFFERENCE IN WING LENGTH 271 



of environmental effects from bottle to bottle would tend to be 

 equalized in the three sets of offspring. This care was taken 

 because of the marked influence environmental conditions, at 

 least, have upon general body size. 



Delcourt and Guyenot^ have suggested that in my note on 

 the failure of disuse to decrease wing length, I should have given 

 the ratio of wing length to body length. It did not, and still does 

 not, seem to me to be necessary since all the factors involved, 

 except disuse of wings, tended to decrease the general body size 

 as much as or more than that of the wing. In this paper, however, 

 it does seem desirable to have some other character with which to 

 compare the wing. Among all that are feasible the body length 

 is the worst because it may change from hour to hour in the living 

 insect, can be measured only with great difficulty and changes 

 greatly after death. I have used the length of the middle femora 

 because it has none of these disadvantages. The wings and legs 

 used here were removed from freshly etherized flies and immedi- 

 ately mounted in balsam. Measurements were made and are 

 recorded in units of t6 mm. for the wings and t^o mm. for the 

 femora. 



Taking up first the offspring of normal females x wingless 

 males, we find that, while the wing is approximately of normal 

 length in both sexes, both it and the femora are significantly 

 smaller than in the homozygous normal material. This may 

 possibly be an environmental effect which was not entirely avoided 

 by the cultural methods used. However, the ratio of the wing 

 to femur is also significantly smaller in both sexes. It is smaller 

 even though, as was pointed out above, there is a tendency for 

 small flies to have the ratio larger than in the case of large flies. 



^ Bull. Scient. France et Belgique, 7th Serie, torn. 45, no. 4. In a general denun- 

 ciation of all the work hitherto done with this insect, they deplore the fact that 

 the results have been obtained without the extreme refinements of bacteriological 

 and physiological methods whioh they recommend. Their criticisms, insofar 

 as they have any value, can be applied only to the study of fluctuating variants 

 such as the characters considered here. All attempts to get heritable abnormal 

 venation or such forms as wingless and miniature by purposely using extreme 

 environmental conditions have failed. It is, therefore, absurd to lay stress in 

 such cases upon the slight variations of environment from bottle to bottle. 



