4 EXPERIMENTS WITH DROSOPHILA AMPELOPHILA. 



DESCRIPTION OF ABNORMAL VENATION. 



It is probable that all insects occasionally show some abnormality of 

 wing- venation. In my experience with Drosophila ampelophila they 

 occur in one-third of 1 per cent of wild specimens. The data concern- 

 ing this point are given in table 1. In these the abnormalities consisted 

 of irregularities of the second longitudinal vein or small dashes near its 

 distal end (similar to figs. 3 to 10). Only one of the 19 abnormal* wild 

 flies I have seen was abnormal in both wings. 



TABLE 1. Percentage of wild Drosophila ampelophila 

 which have extra veins in their wings. 



While rearing this insect for another purpose, several such abnormal 

 specimens were found in one family. My principal abnormal strain, in 

 which the variety and amount of abnormality is little short of astound- 

 ing, came from these. The various figures give a better conception of 

 what was obtained than would verbal description. There is the utmost 

 variation in the abnormal venation, not only in different flies, but in the 

 different wings of the same fly. The majority of the abnormalities are 

 in the distal portion of the marginal cell, but they have been found also 

 in the submarginal and a few in the first, second, and third posterior 

 cells, affecting all the longitudinal veins except the first. 



CORRELATION BETWEEN THE RIGHT AND THE LEFT WINGS. 



One wing may be abnormal, or both may be. In the latter case the 

 abnormality may be great in one wing, small in the other ; on one vein 

 in one wing and lacking on this vein but present on others in the other 

 wing (see figs. 44 to 46) . Nevertheless there is a correlation between 

 the intensity of the abnormality in the two wings, as is made clear by 

 tables 2 and 3. In drawing up these tables the range of variation of 

 the intensity of the abnormality was divided arbitrarily, since the char- 

 acter is not quantitatively measurable, into six classes: normal vena- 

 tion (or zero intensity of the abnormality) , very slight (see figs. 3 to 7) , 

 slight (see figs. 8 to 11), medium (see figs. 12 to 18), great (see figs. 

 19 to 24) , and very great (see figs. 25 to 35) . To which class a given 

 wing should be assigned is a matter of judgment ; but since when these 

 tables were made up it was thought that there was no correlation be- 



*Unless otherwise stated 

 "veins added." 



'abnormal venation" means, throughout this paper, 



