1911] on the Srmts of Battprflioii. 11 



Closely iillied to these tropical and subtropical Orange-tips is a 

 group in which the orange apical patch is replaced by a brilliant 

 crimson. The South African representative of this grou]) has a scent 

 which comes nearest to the garden heliotrope, commonly called "chei'ry- 

 pie." In yet another group we find, instead of orange or crimson, an 

 apical patch of glossy purple. The only species of J'urple-tip which 1 

 have had an opportunity of examining in the living condition is also 

 ])ossessed of a sweet, flowery scent somewhat different from that of 

 the last. 



Many more examples of these perfumed white butterflies could be 

 given, but 1 should only weary you by multiplying cases. For our 

 ])resent purpose it is sufficient to say that among the l)utterflies that 

 ai'e fairly close relatives of our common whites, the odours, though 

 not universal, are very fi'equently present ; that they vary much in 

 character and intensity, though possessing in common an agreeable 

 (piality and a likeness to the perfume of certain vegetable products, 

 particularly to the scent of flowers. They are almost without excep- 

 tion confined to the male sex, and to the upper surface of the wings, 

 and they are almost invariably found in connection with the peculiarly 

 specialised scales that we have learned to distinguish as " plumules." 

 The only exception to the latter statement that I know of among this 

 particular assemblage of butterflies is the yellow African Orange-tip, 

 Tpracolus auxo, in which I find no plume-scales, though it has a 

 flowery odour which in some specimens is really strong. 



Apart, then, from a few possible exceptions, we have certainly 

 established a relation between the presence of plume-scales and the 

 emission of a flower-like odour. AVhat is the nature of this relation ? 

 To answer the question let us examine the plume-scale itself a little 

 more closely. This diagram shows a typical form of plume-scale taken 

 from one of the common African whites, Belenois thysa. This butter- 

 fly, which somewhat recalls one of our common whites, though generally 

 larger, and still more closely resembles Mylothris agatliina lately 

 mentioned, has a strong, sweet odour like that of roses. The scale 

 consists of a flattened plate, or lamina, rounded at the base and sharp 

 at the apex. At the middle of the base is attached a slender foot- 

 stalk, at the end of which furthest from the lamina we find another 

 flattened structure, in this species shaped like a cheese-cutter, which 

 may be called the " accessory disc," or simply the " disc." From the 

 apex arise the cilia-like processes, which may conveniently be termed 

 the " fimbrige." This may serve as an example of a form of plume- 

 scale very commonly found in the white butterflies or Pieriiiae, but 

 the scale in all its parts is liable to considerable modification ; and, in- 

 deed, it may be said with truth that in no two species are the scent- 

 scales exactly alike. The diagrams will show how very diverse are 

 the forms assumed by the plumules of these white butterflies ; but in 

 all of them may be observed under various shapes the lamina, fimbriae, 

 footstalk and accessory disc. The scale is formed of chitin, a sub- 



