The Bionomics of South African Insects. 429 



the broad band becomes sharply defined on its outer border, 

 bnt lacks the light tint of the full wet phase. 



These considerations and the careful comparison of Figs. 

 5 to 8 on Plate XIII will show the essential nature of the 

 changes by which the cryptic under-side of the dry phase 

 is converted into the startlingly conspicuous under-side of 

 the wet phase, or vice versa. The niid-rib-likc stripe 

 widens, lightens in tint, becomes sharply defined along its 

 outer border, and is now the " warning band" of pclasgis. 

 The row of ocellated spots, many of which, with semi- 

 transparent white centres and specially-coloured borders, 

 suggest holes in the apparent leaf of archesia, become 

 entirely or almost entirely black upon the hind-wing, and 

 gain intensely black borders upon the fore-wing of |;c/a,s//is, 

 and, placed upon the light ground of the " warning band," 

 render this feature still more conspicuous. The mottling 

 disappears, and the ground-colour, both within and without 

 the borders of the " warning band," becomes an almost 

 uniform very dark brown, forming a most effective contrast 

 with the band. Finally, the dead-leaf-like margin of the 

 wing of archesia is rendered conspicuous in 'pclasgis by a 

 black-and-white fringe and two parallel scries of light 

 markings just within and parallel to the much less deeply 

 indented outline. 



Furthermore, the comparison of Figs. 6 to 8 on Plate 

 XIII with Fig. 5 on Plate XII shows clearly enough that 

 the under-side of the dry phase of archesia differs from its 

 upper-side in being cryptic, while the comparison of Fig. 5 

 on Plate XIII with Fig. 4 on Plate XII shows that the 

 under-side differs from the upper-side of the wet phase 

 (■pelasgis) in being more conspicuous, thus in both respects 

 acting like the two phases of sesamns and antilo'pe. The 

 under-side of iKlasgis is more conspicuous than its upper- 

 side because of the increased lightness and greater sharp- 

 ness of the borders of the band and the greater contrast 

 afforded by a darker ground-colour, also because of the 

 more ])ronounced light marginal markings. 



I have described the relationship between the phases of 

 archesia at some length, because it was the consideration of 

 this species which first convinced me of the validity of the 

 interpretation here set forth, that we have convincing 

 evidence of natural selection acting in two opposite direc- 

 tions in the two phases — -in the one to produce the maxi- 

 mum of concealment, in the other a very efficient form of 



