I'.lll] on the Scents of Butterflies. 81 



forewing. When emission of the scent is required, a, slight separation 

 of the fore and hind wings gives it exit. The special distribution of 

 trachea3 may he a provision for pumping air into tlie patch from 

 below, and so supplying a vis a tergo to assist the escape of the 

 perfume. 



]\rany other butterflies possess similar patches of scent-distributing 

 scales. They are generally, though not always, so placed as to be 

 covered up' in the ordinary position of the insect. In some instances 

 there are two patches on each side, one on the upper surface of the 

 iiindwing, the other on the under surface of the forewing, these 

 being so arranged' that they exactly cover one another when the 

 butterfly holds its wings in the normal position. It is to be observed 

 that in these patches the rule is for the scent-scales to l)e of the 

 same general character as the ordinary scales of the wing, though 

 they may differ much from the latter in shape, size and arrangement. 

 The patches seldom conttiin plume-scales, and, when fitted with a 

 sliding lid, I believe it would be correct to say that they never do. 

 •■•• ■ The question may be asked : is it not necessary that the scent 

 should be economised in the case of the plume-scales quite as much 

 as in the case of the definite patches ? No doubt it is ; and a little 

 further consideration of the typical plume-scale may show us how 

 this is effected. The plume-scales, it is true, being as a rule generally 

 distributed over the wing, cannot be shut down under a lid ; but 

 they are frequently scattered among ordinary scales which are a good 

 deal longer and larger, and which may act as coverings to the indi- 

 vidual scales, though there is no general covering for the whole. 

 Then again, as we have seen, the plume-scale has an accessory disc 

 and a long footstalk. The disc with its internal chitinous structure 

 may act as a reservoir for the scent ; it will be remembered that in 

 many cases it appears to contain a convoluted tube. The footstalk 

 seems to be flexible, and it often shows one or more sharp bends in 

 its course. These bends may impede the passage of the scent from 

 the reservoir in the disc to the lamina and fimbria, and the butterfly 

 may be able, by some movement of its wings, to bring about a straigh- 

 tening of the footstalk and a consequent liberation of the odour. 

 At any rate, it is probably significant that the apparatus of accessory 

 disc and long flexible footstalk belongs to the plume-scale alone. 



There is a handsome butterfly, common in Africa, which is not 

 far removed in affinity from our well-known "Brimstone." This 

 butterfly, which is known as Catopsilia florella, has in the male a 

 strong fragrant scent. Now Catopsilia florella possesses on the hind- 

 wing a patch of special scales which is somewhat similar in aspect 

 and position to the scent-patch in the Tlouded Yellow. But, curiously 

 enough, the characteristic scent appears to proceed, not from th.e 

 patch on the Iiindwing, but from another structure altogether. This 

 is a beautiful silky fringe of long hair-like scales which are set along 

 the edge of the forewing on its underside, and are covered as a rule 



Vol. XX. (No. 105) g 



