74 Mr. F. A. Dixey '[March 3, 



odourless. On applying the microscope to the scraping which carries 

 the scent, we find at once an answer to our question. The great 

 majority of the scales are of the ordinary well-known kind, consisting 

 of an elongated flattened lamina, provided at one end with a short 

 quill-like footstalk by which they are attached to the membrane of 

 the wing, and frequently showing at the other extremity a more or 

 less marked indentation. But among these will be found certain 

 scales of an entirely different appearance. These latter scales in the 

 insect before us are somewhat heart-shaped, carrying a long footstalk 

 which ends in an almost circular disc, and tapering at the other 

 extremity to a point. But the greatest peculiarity of these special 

 scales is to be found in the plume-like structure which crowns their 

 apical portion. Under a low power of the microscope the appearance 

 is that of a tuft of fine transparent hairs, strongly suggestive of the 

 vibratile cilia which are so familiar in animal and vegetable histology ; 

 but these hair-like processes, unlike the cilia, have no faculty of 

 active movement, and under a high power they bear rather the aspect 

 of minute tubes, in many cases seeming to be open at their free 

 extremity. On examining a similar scraping from the under surface 

 of the male, or from either surface of the female wing, we find only 

 scales of the ordinary kind ; the special " plume-scales," as they have 

 been called, being invariably absent. Inasmuch, then, as the charac- 

 teristic fragrance is found only in scrapings wnich contain the plume- 

 scales, we are justified in concluding that these remarkable structures 

 act as carriers of the perfume. 



So far we have considered only one species of butterfly, the 

 common Green-veined White ; but the question will naturally be 

 asked — what about other butterflies, the other common whites, for 

 example ? Is this flowery perfume a peculiarity of one species only, 

 or is the property of emitting a fragrant odour shared by other 

 related insects .'' In order to answer this question, let us suppose 

 that we make a series of trials on the second species of smaller 

 common White, the small Cabbage or Garden White, as it is usually 

 called. Here, again, no trace of a flowery odour is discoverable in 

 the female or in scales from the lower surface of the wings in the 

 male ; but, as before, the upper surface of the wings in the latter 

 sex will be found to be scented, and, also as before, the scent will be 

 found to adhere to the scales removed by scraping or brushing from 

 the upper surface. Examining the scented scraping microscopically, 

 we find that here, too, are a number of plume-scales mixed in with 

 scales of the ordinary type. These plume-scales bear a family resem- 

 blance to those of the previous species, but are easily distinguishable 

 from them (see the diagr<im). In fact, it is quite as easy, perhaps 

 easier, to discriminate between the two species of common white by 

 comparing two scales measuring not much more than one-tenth of a 

 millimeter in length, as it is to tell them apart by examining entire 

 specimens of both insects. 



