THE EVOLUTION TIIEOin" 



nowluTi' waulinu-. wIi.mv tlic under side is protectively coloured at all, 

 but in many easi's the protective colouring spreads over almost the 

 Avhole of the anterior win^-.s, and these are then not folded far back 

 when at rest, as will be seen later in the so-called leaf-butterllies. 



There is one <jenus of diurnal butterflies which seems to contra- 

 dict the law that all the surface that is visible in the resting position 

 exliibits tlu' protective coloration — the South American wood- 

 buttertiies of the genus Ageroiiia. They have on the upper surface 

 a very complicated bark-like pattern of mingled grey on grey, and 

 this confirms the usual rule, for we know that these butterflies— 

 a striking exception among all the other diurnal forms— settle with 

 outspread wings on the trunk of a tree in exactly the same attitude 



Fig. 9. Eebomoja glaucippe, from India ; under surface. A, in flight. B, in resting 

 attitude. 



as many of the nocturnal Lepidoptera of the family of the 

 Loopers or GeometridaB, in which the upper surface is also deceptivel}- 

 like the bark of the tree on which they rest. 



In all the nocturnal Lepidoptera it is the upper side of the wing 

 which is sympathetically coloured, if protective coloration has been 

 developed at all. In all the Sphingidit^, many ' Owls ' and Bomby- 

 eidse, the anterior wings are grey banded with darker zigzag lines, 

 and mottled with many shades of black, grey, yellow, red, and even 

 violet. As the anterior wings cover the body and the posterior wings 

 like a roof, they make the resting insect very inconsj)icuous when 

 it has settled on wooden fences, trunks of trees, or even old timber. 

 When bright colours — red, yellow, or blue — occur in these moths 



