ix RECOGNITION-MARKS 169 



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 

 differentiation 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 utilised for securing the safety of the perfect insect to a 

 sufficient extent to provide for the continuance of the race, 

 thus keeping up that endless variety of form and colour 

 which is, perhaps, one purpose of their existence. 



The first great adaptation here, as throughout nature, is 

 to secure concealment from their most dangerous enemies, 

 and this is effected by various kinds of protective, deceptive, 

 or warning coloration which in some form or other pervades 

 the whole order, and forms a most fascinating subject of 

 study. The protective coloration is mostly on the under 

 sides of the wings of butterflies, and on the upper sides of 

 the upper wings of moths, the parts respectively exposed to 

 view when the insect is at rest. Great numbers are also 

 deceptively coloured by eye-marks (ocelli), which resemble 

 the eyes of mammals in such a way as to be very striking in 

 the mingled light and gloom of the forest and in the general 

 surroundings of each species. Large groups in all the 



