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 Heliconidse, the 
Danaidse, the Acraeidse, 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 Nymphalidae, 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 
