INTRODUCTION. XV 



(7). FOLDS OF THE WING MEMBRANE. These are not at all of un- 

 common occurrence in the males of certain species, and are frequently 

 closely connected with scale patches, the peculiar fold in Laertias on 

 the inner border of the hind wings of the male which covers a patch 

 of scales, having been already referred to. In our British families, 

 the TORTRICES exhibit the character most markedly along the costa of 

 the fore wings. In the males of many species in this group the mem- 

 brane is folded back on itself and thus increases the wing expanse 

 very strikingly. This character is not even of generic value, the 

 males of most closely allied species being without or with this pe- 

 culiar development, although Wilkinson founded his division Plicatce 

 on the character. It is remarkable, however, that the males of most 

 of the folded species are remarkably active and the greater wing 

 expanse may thus be of service. Such examples occur in many 

 species of the genera Tortrix and Dichrorhampha, Ptycholoma lecheana 

 etc. Closely allied to the folds of membrane on the margins of the 

 wing is the presence of an extra winglet or lobe attached to the base 

 of the normal hind wings in the species of the Geometrid genus Lolo- 

 pophora. These are of the same membranous structure as the hind 

 wings, and in L. sexalisata and hexapterata are fringed and very 

 conspicuous. These two species also fly very rapidly in the evening 

 over the tops of tall bushes etc., and as the hind wings are unusually 

 small, the suggestion at once occurs that the extra wing area is needed 

 to aid their flight. 



(8). VENATION. We occasionally find the venation giving traces 

 of sexual dimorphism, but venation is in itself so variable a factor that 

 many exact experiments are needed to show which aberrant forms are 

 due to chance, and which are the result of sex. In genera such as 

 Aphomia where the cell of the fore wings differs in size, there is a 

 distinct sexual difference in the venation. Scudder says : " The 

 difference in the direction of the veins of the wings in the sexes is 

 slight, and concerns the point of origin of one or two of the upper 

 branches of the sub-costal vein of the front wings ; but occasionally 

 it is very marked, as in many of the " hairstreaks," where the branches 

 of the sub-costal vein near the end of the cell are thrown far out of 

 place to accommodate a patch of peculiar crowded scales. This patch 

 itself, moreover, is a feature of the males alone and occurs in many 

 " hairstreaks," where the position of the vein is not altered " (p. 872). 



(9). LEGS. Sexual dimorphism frequently exhibits itself in the 

 structure of the legs. I have previously referred to the development 

 of tufts of scales on the hind legs of certain species in the genus 

 Acidalia and to somewhat similar tufts on the fore legs of the species 

 of Herminia. The aborted hind legs of the male of Hepialus hectus, 

 which is supposed to be a scent gland, has also been previously 

 mentioned. In many species, as Lobophora, the spurs on the hind legs 

 of one of the sexes are "absent or aborted, whilst the essential difference in 

 the structure of the fore legs of the sexes in the Erycinidce, Lyccenidce, and 

 Nymphalidce is well known. Scudder says : " Sexual dimorphism shows 

 itself in the legs, in the proportional length of the different pairs in 

 the two sexes, in the special development of certain joints, in the 

 appendages and in the clothing. It appears remarkably in the ap- 

 pendages of the two higher families of butterflies Nymphalidce and 



