92 



the variability of many of these different orders ? And what 

 of the neuration of the Syntomidce ? There is hardly a family 

 which can compare for variability in this respect. The 

 discoidal cell may be large or small, normal veins may be 

 missing, or they may vary their position to a remarkable 

 degree. 



I will mention but one or two further cases of species that 

 are well known to all of you. Take the species of Argynnis 

 ■ — papJiia, adippc, or aglaia : they have a strong, powerful flight. 

 The two Brenthis species, euphrosyne and selene, although 

 from the size of the insects they necessarily have less power, 

 are still species with much the same flight. These two 

 genera have the same neuration. But compare the flight 

 and neuration of the species of Melitcea. The flight is 

 markedly different and is not nearly so rapid, and the 

 neuration has differences in both fore- and hind-wing. The 

 hind-wing has lost the discocellular, and the cell is open, as 

 against a closed cell in A rgynnis. Exactly the same difference 

 is to be found in the hind-wing between such genera as 

 Vanessa with the species iirticce, polychloros, and io, Polygonia 

 c-alhinn, and Pyrameis cardiii on the one hand, and Limenitis 

 Sibylla on -the other. Robustness of build, and strength of 

 the actual veins themselves, unquestionably account in some 

 measure for some of the differences in flight. Limenitis 

 Sibylla and Apatuva iris are not at all alike in their habits or 

 strength of flight, and there is this important neurational 

 difference between them, namely, that L. sibylla has only 

 the cell of the hind-wing open, whereas the cell of both fore- 

 and hind-wing in A. iris is open. This structural difference 

 alone would in all probabilit}' have been attended by some 

 difterence in flight, but with the added difference in build the 

 disparity is greatly accentuated. 



I have been at some pains to show that flight is to a large 

 extent correlated with the neuration of the wing, and that 

 when we are able to appreciate differences in flight there is 

 an accompanying difference in neuration. Nearly all the 

 veins of the wings (but particularly the hind-wing) are able 

 to undergo modification in strength, or position, or even 

 both. Some veins are much more variable than others. 

 Vein 5 of the hind-wing is probably the least stable part of 

 the structure, whereas vein 8 is exactly the reverse. In the 

 fore-wing vein 5 is most constant, while 7, 8, g, 10 are van- 

 able. It must be manifest from the nature of the structure that 

 for the delimitation of genera without an appeal to other bio- 

 logical characters it is not absolutely reliable. Species having 



