322 COLOUR IN NATURE chap. 



organisms and their surroundings or between un- 

 related organisms is denied by no one ; it is the 

 explanation involved in the use of the terms " pro- 

 tective " and " mimicry,'' which is doubtful. 



It would lead us too far to enter in detail into 

 all the arguments which have been advanced as 

 tending to prove that the resemblance between 

 organisms and their surroundings has been acquired 

 and is maintained by the aid of Natural Selection ; 

 the following summary of the facts in the case of 

 the Lepidoptera, taken from Weismann, is sufficient 

 for our purpose here. 



Weismann states the case as follows : — " Im- 

 mune" butterflies, such as the Heliconidae, the 

 Danaidse, the Acrseidse, the Euplocidae, have usually 

 both surfaces of their wings coloured alike, and never 

 resemble their surroundings in the resting position ; 

 unprotected butterflies, such as the Nymphalidse, are 

 in the great majority of cases protectively coloured 

 on their lower surface. Further, the coloration of 

 this lower surface bears a close relation to the 

 position of the wings in repose — that is, if in this 

 position the hind wings overlap the fore, it is only 

 the exposed tip of the fore-wing which is protectively 

 coloured ; while if, as in Kallima, there is no over- 

 lapping, the whole under surface of the fore-wings 

 displays' this type of coloration. Again, the special 

 type of protective coloration which consists in 

 resembling a leaf, is exceedingly common among 

 wood-inhabiting butterflies whether related or not. 

 This coloration bears no definite relation to the 

 structure of the wing, but " die Flache behandelt als 

 eine tabula rasa, auf der man zeichnen kann, was 



