182 THE WORLD OE LIEE 



the sexes in many butterflies this adds to the difficulty of 

 supposing vision to be the 'primary means of recognition. But 

 it may be a secondary means. It is well known that in some 

 moths the females attract males by scores at night, and this 

 can only be by scent, or something analogous to it. It is 

 also known that the males of manv butterflies emit a strong 

 perfume which has been traced to certain peculiarly formed 

 scales on the wings. Scales, apparently of a similar nature, 

 have been found in several distinct families of butterflies and 

 moths, and it seems probable that the function of these is 

 in all cases to produce a perfume agreeable to the other sex, 

 though only in a few cases is such perfume perceptible to 

 us. 



It seems probable, therefore, that the sexes of Lepidoptera 

 are mutually attracted by a perfume agreeable to each other, 

 but disagreeable or neutral to others of the same sex or to 

 other species. Each time this attractive odour was perceived 

 and the source of it traced, the visual image of the insect 

 would be connected with the smell, and thus only would the 

 colour and markings of the species become known and be 

 distinguished from that of other species. This being the 

 case, we see that the complete scaly covering of so many of 

 these insects serves a double purpose. It affords the means 

 of using an extended surface for the highly important scent- 

 glands, which, by serving to bring together the sexes of each 

 species and to prevent intercrossing, would facilitate differ- 

 entiation and lead to that wonderful diversity of colour and 

 marking accompanying comparatively slight differences of 

 structure for which this order is so remarkable, and which are 

 absolutely unequalled in the whole animal kingdom. This 

 variety of colour, rendered possible by the large wing-surface 

 covered with small but exquisitely organised scales, is util- 

 ised for securing the safety of the perfect insect to a sufficient 

 extent to provide for the continuance of the race, thus keep- 

 ing up that endless variety of form and colour which is, per- 

 haps, one purpose of their existence. 



