It can be proved, however, that such transmissions may, in the course of many successive generations, become intensified until the characters are exhibited by the females in the same degree as in the males. I know no better example of this than that afforded by the beautiful butterflies of the genus _Lycæna_. In this genus, which is rich in species and widely distributed over the whole earth, and must therefore be an old one, the upper surface of the wing is blue in by far the greater number of species, at least in the male sex. But there are three or four species which are dark-brown, and quite or nearly alike in the two sexes; such are the species _Lycæna agestis_, _L. eumedon_, _L. admetus_, and others. Everything indicates that this is the primitive colour of the genus. Moreover, there are some species with brown females, in which the males are not completely blue, but which have a slight bluish tinge, like _L. alsus_, the smallest of our indigenous Blues. Then follows a host of beautiful species, like _L. alexis_, _L. adonis_, _L. damon_, _L. corydon_, and many others, with brown females, and among these there occasionally occur females more or less tinged with blue. These lead on to _L. meleager_, which has two forms of female, a common brown and a rarer blue; and thus we reach _L. tiresias_, _L. optilete_, and _L. argiolus_, in which all the females are blue, although less intensely and completely so than their mates. The climax of this evolutionary series is reached by some species like _L. beatica_, belonging to tropical or at least warm countries, in which both sexes are of an equally intense blue. As we know that, in species with an excess of males, sexual characters always begin in the males, there can be no doubt as to the direction of evolution--from brown to blue--in this series. Furthermore, the entire absence of scent-scales in most of the species with brown males indicates the great age of these species, for, as far as I have been able to investigate, all the males of the blue species possess them.