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observe that the incidence of seasonal dimorphism is often different 

 as between the sexes ; the cryptic coloration, usually more perfect 

 in the female than in the male, being in the case of the former sex 

 frequently prolonged into the wet season, at which time the latter 

 sex has lost it completely. 



Let me give a few examples. There are two pretty species of 

 the genus Teracoliis, known as I. i)iiellaris and T. phimdia 

 respectively. In both of these, vv^hich inhabit dry and sandy 

 localities in north-eastern Africa and western Asia, the female 

 retains at all seasons a reddish, sand-coloured underside. The 

 underside of the male of T. pnellaris in the dry season is similarly 

 coloured ; in the w^et season it is bright yellow. The male of T. 

 phisadia is similarly bright yellow beneath in the wet season ; in 

 the dry season it may either retain its bright yellow hue, or maj' 

 become sand-coloured like the female. The underside in both sexes 

 of 'Uevacohix, aK.ro, a well-known butterfly in South Africa, is in the 

 dry season coloured like a dead leaf ; the resemblance being 

 increased by a leaf-like modification of shape, best marked, be it 

 observed, in the female. In the wet season, though the leaf-like 

 contour is lost in both sexes, the female retains some of the cryptic 

 coloration which is at that period quite absent from the male. A 

 similar description will apply to an interesting butterfly from the 

 New World ; I'l/risitia jnoterpia of Central and South America. 

 Here the leaf-like " uncination " or " hooking " of the wings, in 

 what appears to be the dry-season form, is carried to a still greater 

 extent, and in the female is especially remarkable. In addition to 

 the uncination of the forewing, the hindwing is in this sex pro- 

 longed into tails which may stand either for the stalk, or, as is 

 perhaps more probable, for the sharp apex of the leaf to which the 

 colouring of the underside affords so close a resemblance. The male 

 shows a tendency in the same direction, but to a considerably less 

 extent. In the wet season neither sex exhibits uncination or is 

 furnished with tails, but the female is duller in hue beneath, and 

 less conspicuous than the male. 



Finally, as exemplifying the same principle of superior advan- 

 tage to the female manifesting itself in a diflerent way, we may 

 take the curious instance of Bdenois tlujsa, an African butterfly 

 which mimics the well known and prevalent Mi/lot/tri.'> of/atliina. 

 In the dry season the mimicry is extremely good, the resemblance 

 being, as Mr. Trimen says, "deceptively close in both sexes," the 

 male copying the male Mi/lot/tris, and the female the female. In 

 the wet season the mimicry is a good deal less exact, and the 

 female Belenois often loses her special resemblance to the female 

 Mi/lothru altogether ; becoming merely, like her mate, a rather 

 rough copy of the male I\Iylot/iris ai/athina. 



Putting all these facts together, we may, I think, consider that 

 we have gained, not indeed a complete explanation, but some light 

 on the facts of butterfly Dimorphism, whether seasonal or sexual. 



