August 3, 191 1] 



NATURE 



165 



plume-scales bear a family resemblance to those of the 

 previous species, but are easily distinguishable from them. 

 In fact, ii is quite as easy, perhaps easier, to discriminate 

 between the two species of the common white by com- 

 paring two scale-, measuring not much more than one- 

 tenth of a millimetre in length, as it is to tell them apart 

 b] examining entire specimens of both insects. 



We conclude, then, that the scent-producing function is 

 essentially similar in the two kinds of smaller common 

 white. But it is to be observed that the endowments of 

 Ih'- two in this respect, though similar, are not identical. 

 The scent of the green-veined white (Ganoris napi) is, so 

 far as my experience goes, always present and easily 

 recognisable, this being the reason why I chose it for first 

 mention. But with the common garden white (Ganoris 

 rapae), the case is different. You will probably find some 

 male specimens with no appreciable scent at all ; others 

 with tlie scent so faintly developed that you may be 

 doubtful about its presence; in none, probably, will the 

 scent be nearly so strong as in the case of the green-veined 

 white that we began with. Moreover, the character of the 

 perfume differs. It has been not inaptly compared to 

 sweetbriar, and it is at all events quite distinct from that 

 of its near relation Ganoris napi. Extending our observa- 

 tions 10 the lar^e cabbage white (Ganoris brassicae), we 

 find a plentiful supply of plume-scales of quite a different 

 aspect, these being very much longer, tapering gradually 

 from base to apex, and showing none of the elegant heart- 

 shaped outline that we saw in the other two species. The 

 regularly disposed fringe or plume of the smaller whites is 

 here also replaced by a kind of untidy bundle. These 

 scales, again, are present only in the male, and only on 

 the upper surface of fore and hind wing. What about the 

 scent? It cannot be said to be entirely non-existent, but it 

 is certainly the case that anyone of average olfactory 

 powers ma;' examine many male specimens of the large 

 white without being able to detect any characteristic odour 

 whatever. In some individuals, however, it is unquestion- 

 ably present, though it is, as a rule, only to be appreciated 

 with difficulty. But when detected it is like- a faint whiff 

 of violet powder, or, as has been happily suggested by 

 Dr. Longstaff, orris-root. 



There is in Africa a well-marked genus of white 

 butterflies which goes by the name of Mylothris. The 

 members of this group are in many respects much like 

 the common whites of our own country : they are, however, 

 as a rule somewhat brighter in appearance, many of them 

 having a touch of vermilion, orange, or some shade of 

 yellow al tin base of the wings close to the bodv. This is 

 more frequent on the under surface, but in many cases it 

 is seen on tlie upper side as well. The genus also differs 

 from our common whites in usuallv possessing a distinct 

 marginal row of dark spots. The figures shown on the 

 screen, which were photographed in colour from nature, 

 were prepared for another purpose ; they give, however, a 

 good idea of the general features of the group. 



Now all the species of Mylothris which I have had the 

 opportunity of examining during life possess a strong and 

 fragrant odour, which is developed under just the same 

 conditions as in the butterflies we have alreadv discussed. 

 That is to say, it belongs to the male alone, and in that sex 

 is confined to the upper surface of the fore and hind wings. 



The s,ent of Mylothris agathina t a species which is 

 abundant in many parts of Africa south of the Sahara, 

 appears to me to be exactly that of sweetbriar. It is a 

 good deal like that of our garden white (not the 

 veined Species), but very much more intense. Indeed, >,, 

 powerful is it, that I have more than once perceived it 

 when the butterfly was held in the hand at some consider- 

 able distance. 



There is a pretty species of Mylothris which T found 

 rather common at East London (South Africal. It has been 

 named trimenia, after the distinguished naturalist who 

 presided for many years over the South African Museum at 

 Capi rown. It has a graceful, floating flight, and the 

 hindwings in the male are of a delicate lemon-yellow. The 

 general attractiveness of this insect is increased by its 

 pleasant fragrance. This is quite different from the odour 

 of its congener affathina, though at least equallv powerful. 

 It is not easy to describe, but may perhaps best be com- 

 pared 10 tli,- scent of sweet-oea or clover, with a sue. 

 of orange-peel or lemon. The females of both these species 



no. 2179, vol. 8;] 



of Mylothris are destitute of odour. The curious shape of 

 the male scent-scales, which is tolerably uniform throughout 

 the genus, is shown in an outline diagram. 



In a couple of months' time our country lanes will be 

 enlivened by the presence of a butterfly known no doubt 

 to many of you as the "orange-tip." This very pretty 

 insect is much like one of our common whites, but may be 

 distinguished by the elaborate green mottling of portions of 

 the under surface — a feature of colouring which causes the 

 butterfly to be almost invisible when it settles with closed 

 wings on the head of an umbelliferous plant. This green 

 mottling is found in both sexes, but the male has in addition 

 .1 large patch of bright orange at the apex of the forewing. 

 Whether this butterfly is scented I am unable to say, as I 

 never happen to have had the opportunity of examining 

 live specimens since I began to search for butterfly odours, 

 but the male certainly possesses plume-scales of the same 

 general character as those of the common whites, though 

 differing, as will be seen by reference to the diagram, in 

 points of detail. I should be glad to receive information as 

 to its power of scent-production from any of you who may 

 make the acquaintance of the butterfly during the coming 

 spring. 



Though I have at present no information on this point as 

 to our English orange-tip, I have been able to test several 

 foreign species which are somewhat like it in aspect, and 

 are not verv far removed from it in point of affinity. These 

 belong to the genus Teracolus. One of these Teracoli, 

 called omphale. common in Africa, has a scent which I 

 compare to that of Philadelphus, commonly called 

 " Syringa," or perhaps more exactly to that of the white 

 lily, together with a more aromatic constituent suggesting 

 at one time chocolate, at another, musk. A second African 

 orange-tip, Teracolus achine, has a scent, not always 

 pies, nt, which reminds me of honeysuckle. The scent of 

 a third African species, Teracolus auxo, in which the 

 general coloration is yellow instead of white, recalls that 

 of jasmine or Philadelphus. 



Closely allied to these tropical and subtropical orange-tips 

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

 .1 brilliant crimson. The South African representative of 

 this group has a scent which comes nearest to the garden 

 heliotrope, commonly called " cherry-pie." In yet another 

 group we find, instead of oMnge or crimson, an apical 

 patch of glossv purple. The only species of purple-tip 

 which I have had an opportunity of examining in the 

 living condition is also possessed of a sweet, flowery scent 

 somewhat different from that of the last. 



Many more examples of these perfumed white butterflies 

 could be given, but I should only weary you by multiplying 

 cases. For our present purpose it is sufficient to say that 

 among the butterflies that are fairly close relatives of our 

 common whites, the odours, though not universal, are very 

 frequently present: that they vary much in character and 

 intensity, though possessing in common an agreeable 

 quality and a likeness to the perfume of certain vegetable 

 products, particularly to the scent of flowers. They are 

 almost without exception 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." 

 inly exception to the latter statement that I know of 

 among this particular assemblage of butterflies is the 

 yellow African orange-tip, Teracolus auxo, in which I find 

 no plume-scales, though it has a flowery odour which in 

 some specimens is really strong. 



\p.irf. 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. What 

 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 butterfly, which somewhat recalls one of our common 

 whites, though generally larger, and still more closely 

 resembles Mylothris ag'athina lately mentioned, has_ a 

 Strong, sweet" odour like that of roses. The scale consists 

 el a 'flattened plate, or lamina, rounded at the base and 

 sharp at the apex. At the middle of the base is attached 

 a slender footstalk, 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 " 



