80 Mr. F. A. Dixoy [March 3, 



the only structures by which the scents of butterflies are distributed ? 

 They are by no means the only ones. There are many other methods 

 of distribution of these flower-like odours, some of which we can find 

 without going beyond the group of so-called white butterflies, or 

 Pierines. Visitors to the south coast of England in the late summer 

 and autumn months can hardly have failed to notice a very active 

 butterfly of a fine bright orange colour with a dark border, which 

 is especially given to haunting fields of lucerne and clover. This is 

 the butterfly commonly called the " Clouded Yellow," one of the most 

 conspicuous of the whites, or, as we ought rather to say, the Pierine 

 butterflies. In this insect we should search for plume-scales in vain ; 

 but on examining in a male specimen the front edge of the hindwing 

 where it is overlapped by the forewing, we find on the upper surface 

 a patch of scales distinguished from their surroundings by their 

 lighter colour. The microscope shows that these scales are of a 

 different shape from those of the rest of the wing, and are packed 

 much more closely together ; moreover, instead of lying nearly flat 

 upon the wing, like the tiles on a roof, they are set up on end, some- 

 times almost at a right angle. When the wing membrane is denuded 

 of scales and examined with a high power, the situation of the patch is 

 easily recognisable by the crowding together of the sockets for the 

 insertion of the footstalks, and also by the fact that tracheal, or air- 

 tubes, are seen to be leaving one of the main "veins" of the wing 

 and supplying this particular area, breaking up into smaller branches 

 as they go. 



Under ordinary circumstances the scent of the Clouded Yellow is 

 not easily detected ; but if in a living specimen the scales be scraped 

 off one of the patches that have just been described, they will in 

 many cases be found to have an odour which is somewhat like that of 

 the garden heliotrope, or " cherry-pie." The South African Clouded 

 Yellow, which is much like ours, though quite distinct, has a similar 

 patch and a similar odour. The scent-producing apparatus in these 

 Clouded Yellow butterflies presents many features of interest ; in the 

 first place, the scent-scales are crowded together into one small area, 

 instead of being generally distributed over the wing-surface as in the 

 common whites. Then the scales are quite unlike plume-scales, having 

 neither fimbria} nor accessory disc, while the footstalk is short and 

 quill-like, instead of being long and flexible as in the plume-scales. 

 They are, indeed, quite of the type of the ordinary scales, except that 

 they differ a little in size and shape from tlie scales of their immediate 

 surroundings. The distribution of trachea, or air-tubes, to the site 

 of the scent patch is noteworthy, and so also is the fact that under 

 ordinary circumstances the patch is covered by the overlap of the 

 forewing, which acts like a sliding lid. It may reasonably be conjec- 

 tured that this arrangement ensures economy of the perfume. The 

 production of the scent is confined to a limited area, and its escape is 

 prevented under ordinary conditions by the overlapping edge of the 



