87 



supplementar}' characters, is of great value in determining 

 the family to which a given insect belongs. Certain veins 

 are subject to a great amount of variation, while others 

 remain most constant. There is vastly more variation in the 

 neuration of the hind-wing than in the fore-wing ; and this 

 may be due either to variable ways of folding the hind-wing, 

 or to a varied value as a means to flight, and, perhaps, may 

 sometimes be the outcome of both. 



The most constant veins of the fore-wing are : Vein 2, 

 which hardly varies at all ; vein 12, which scarcely varies in 

 position, except in the Satyridce, where its position is of 

 family value ; while vein 5 and vein i a, b, or c only vary 

 between one family and another, except in the SyntomidcB, 

 where either one, two, or three of these basal veins can be 

 present. In the hind-wing vein 2 is, again, hardly a variant 

 at all, and in yEgeriidcB vein 8 and la, b, or c only vary 

 between one family and another ; only in the Syntomidce is vein 

 8 absent, and this is a family characteristic of the group. 

 All the other veins are subject to much more variation in 

 strength and in position. Vein 5 of the hind-wing is in many 

 families extremely variable, and is sometimes very w^eak or 

 represented by a fold, or even absent altogether. It is signi- 

 iicant that what we call vein 5 of fore-wing is very constant, 

 while what we call vein 5 of hind-wing is very variable. 

 A\'ithin the limits of families we very rarely find veins 

 missing, with the exception of the very variable vein 5 of the 

 hind-wing. In the family Syntoniidce, which is quite 

 abnormal in the amount of variation the species present, any 

 of the veins 2, 3, 4, 5, or 7 may be absent in the hind-wing. In 

 some genera there are not more than five veins present, 

 veins 4 and 7 being absent from a number of genera, as well 

 as vein 8 being wanting, which is common to all the 

 species. 



How is it that all this variation in the neuration has 

 arisen ? Two insects can appear to be almost identical, such 

 as in very many of the wonderfully close resemblances we 

 know of in mimicry, yet the neuration is always different. 

 With varying habits and varying flight we get varying 

 neuration. It cannot, of course, be argued that the flight 

 and habits are as varied as the neuration is, and conversely 

 there are, doubtless, cases where two insects of different 

 neurational structure have the same flight. 



These statements are made only so far as our limited 

 sense of appreciation of such a difficult subject as flight goes. 

 We are only able to appreciate what are probably consider- 



