This conclusion is furthermore confirmed by the fact that, in the male sex, numerous species of butterfly possess another means of exciting the females, namely, by pleasant odours. Volatile ethereal oils are secreted by certain cells of the skin, and exhale into the air through specially constructed scales. Usually the apparatus for dispersing fragrance occurs on the wing in the form of the so-called scent-scales (_Duftschuppen_), peculiar modifications of the ordinary colour-scales of the wing, but sometimes they take the form of brush-like hair-tufts on the abdomen, and they are in all cases so arranged that the volatile perfume from the cells of the skin penetrates into them, and then evaporates through very thin spots on the surface of the scale, or through brush-like, expanded fringes on their tips. Many of these have long been known to entomologists, because their divergence in form from the ordinary scales attracted attention; and it was also observed that they never occurred on the females, but only on the males. Their significance, however, remained obscure until, by a happy chance, Fritz Müller, in his Brazilian garden, discovered the fact that there are butterflies which give off fragrance like a flower, and then close investigation revealed to him the connexion between this delicate odour and the so-called 'male scales.' One can convince oneself of the correctness of the observation even in some of our own butterflies by brushing the finger over the wing of a newly caught male Garden White (_Pieris napi_). The finger will be found covered with a white dust, the rubbed-off wing-scales, and it will have a delicate perfume of lemon or balsam, thus proving that the fragrance adheres to the scales. [Illustration: FIG. 54. A portion of the upper surface of the wing of a male 'blue' (_Lycæna menalcas_); after Dr. F. Köhler. _bl_, ordinary blue scales. _d_, scent-scales. Highly magnified.] [Illustration: FIG. 55. _Zeuxidia wallacei_, male, showing four tufts of long, bristle-like, bright yellow scent-scales (_d_) on the upper surface of the posterior wing.]