( xci ) 



question as it affects the insect-fauna of these islands. With 

 this view I have brought some selected specimens here to-night, 

 and propose, Avhile enlarging the scope of inquiry in one way, 

 to narrow it in another by coniining my illustrations to the 

 group of Pierinse. 



"A substitution of dark pigment for light may take place — 



"(1) Between allied species, as Belenois mesentina, Oram., 

 and B. raffrayi, Oberth. 



" (2) Between nearly-related forms of the same species, as 

 Eronia cleodora, Hlibn., from East London, and E. cleodora, 

 f. dilatata, Butl., from Mombasa. 



" (3) Between the sexes of the same species, as Delias 

 iriferna, Butl., S and 9 • 



" (4) Between individuals of the same sex of the same 

 species, as the ordinary and ' white ' form of Colias electra, 

 Linn., $ . 



"It is often possible to trace a connection between dark 

 pigmentation and certain external or internal conditions, such 

 as horizontal or vertical distribution, season and sex. Can any 

 of these conditions be regarded as a direct cause of melanism 1 



" (1) As instances of the influence of horizontal distribution, 

 or locality, we have Eronia cleodora as above ; Belenois mesen- 

 tina of Africa and India with its Australian representative 

 B. teutonia, Fabr.; and B. severina, Cram., $ from Natal 

 compared with B. severina $ from the Victoria Nyanza. 



" (2) As examples of the influence of vertical distribution we 

 may take Tatochlla autodice, HUbn., ? fi-om Buenos Ayres, 

 and T. stigmadice, Stdgr., ? from the Andes of Ecuador, A 

 familiar case of the same kind is the ordinary Ganoris najn, 

 Linn., $ of Switzerland compared with G. bryonix, Ochs., of 

 the high Alps. 



" (3) To illustrate seasonal influence we may compare the 

 dry- and wet-season forms of Teracolus annee, Wallgrn., 

 T. antigone, Boisd., T. omphale, Godt., Glutojjhrissa saba, Fabr., 

 Appias libythea, Fabr., Tachyris hippo, Cram., Huphina nadina, 

 Luc, H. nerissa, Fabr., and Lxias evippe, Drury. In all these 

 the tendency towards melanism in the rains shown by the 

 females is well marked. The corresponding males are also 

 affected, though in less degree. 



