236 



BRITISH BUTTERFLIES. 



it not probable that this yellow pigment explains the purple colour ? 

 When white light is dispersed by the striae of the scales, may not the 

 yellow light combine with the dispersed blue — its complementary 

 colour — and form white light, whilst the remaining waves of red 

 and violet mix to form the purple we see ? How else can we explain 

 the purple? If this be the case, does not pigment, even in B. qaercus, 

 play by far the largest part in the production of colour ? I may add 

 that the brown scales and yellow scales are different, the brown have 

 teeth, and are more finely striated (in the proportion of 3 to 2) than 

 the yellow; the latter have no teeth, and, therefore, would not scatter 

 the light, but reflect it more in mass ; the striae are also more raised, 

 and the white scale has the appearance of being distended with air. 

 The test as to whether interference is the cause of colour is the 

 variability of the colour at varying angles of the incident light, but, 

 as I have endeavoured to show, in the case of B. onerous, interference 

 alone does not explain the purple gloss, but, plus pigment, it helps to 

 do so (Riding). [See " Discussion on the nature of certain insect 

 colours," Ent. Rec, vi., pp. 204 et seq. ; pp. 255 et seq.] 



Pathological example. — The following is the only specimen that 

 we have noted: — 



Male with a patch of flesh-colonred scales at angle between the outer margin 

 and inner margin of right liindwing (Studd, in I'M., 23, iii, 1907). 



Variation. — The males only vary in the amount and intensity of 

 the purple gloss on the wings, some examples being much brighter 

 than others, i.e., of a slightly more violet tint, and in only two 

 specimens have we seen what may be really termed colour aberrations. 

 These are in the British Museum collection. One is labelled " Veluchi, 

 Greece, 1863," and has the tint, instead of the usual purple, of a pale 

 blue-grey, in some lights almost green-grey =ab. pallescem, n. ab., 

 not unlike that sometimes seen in males of Agriades corydon, the other 

 specimen is from "Jena, 1852"; in this, the tint, although quite 

 pale compared with the type, is yet distinctly of a rather bluer-grey 

 hue than the example from Veluchi. Both these males are beyond 

 average size. The females also differ but little in tint ; occasionally 

 a specimen is of rather brighter violet than usual, and, rarely, one is a 

 shade redder, i.e., the variation is merely slightly in the direction of a 

 bluer- or redder-violet respectively; the area is sometimes slightly 

 increased towards the centre of the wing. Morton records (Ent. Mo. 

 Mag., xxxiv., p. l)^i female in which the violet of the upperside of 

 the forewings is replaced by a beautiful metallic blue, that was taken 

 in July, 1897, in the New Forest. In one specimen in the British 

 Museum collection, labelled " Germany, Leech coll.," the upper 

 portion of the patch, normally found in the discoidal cell, is entirely 

 absent, the lower half, however, normal in tint and extent =ab. semi- 

 obsoleta, n. ab. Raynor states that he has a female, bred at Hazeleigh, 

 July 5th, 1901, in which the purple colour of the forewing is so much 

 reduced as to be hardly noticeable = ab; obsoleta, n. ab. Among the 

 females one finds various stages in tin 1 development of what is known 

 as the bellus form. This latter has three small separate orange-coloured 

 patches towards the upper outer margin of the violet-coloured area. 

 In the British Museum collection is a Large female from Greece, 

 " Veluchi, ISO;-}," with the faintest possible trace of an orange or brown 

 patch just outside the discoidal cell =ab. bellus-obsoletus, n. ab. A 



