THE COLORATION OF ANIMALS 



85 



without saying that the adaptations do not start from a tabula ram, 

 but from what is already present ; of course, natural selection makes 

 use of the markings inherited from ancestors ; it takes what already 

 exists, and alters or extends it as suits best. Thus it is easy to prove 

 that the clear mirrors (Fig. 13, gl 1 and gl 2 ) on the wings of Kallima 

 have arisen from a modification of the nuclei of eye-spots, just as 

 the dark mould-spots which often occur, frequently develop in 

 association with the inherited eye-spots; not always however, for 

 many such accumulations of black scales occur in spots on which 

 there has never been an eye-spot. Thus, too, the 'midribs' of the 

 butterfly have in part 

 arisen from a gradual 

 displacing, extending, and 

 altering of the direction 

 of inherited stripes as, 

 for instance, is clearly 

 recognizable in the pos- 

 terior wing of Fig. 13, but 

 sometimes they are new 

 formations. But the vein- 

 ing of a leaf is never 

 found on the wing of 

 any butterfly of a species 

 which has not the habit 

 of resting among leaves, 

 or which has not had it 

 at one time, and it never 

 corresponds to the natural 

 marking of any genus 

 which does not live in 

 forests. This impression 

 of leaf-venation has ob- 

 viously arisen from quite different patterns of markings, and it has been 

 reached now by one way, now by another. We can see this from 

 the fact that, in different butterflies, it lies in quite different positions 

 on the wing. In the Kallima species the stalk of the leaf lies in the 

 tail of the posterior wing, the tip of the midrib lies near the tip of 

 the wing; in CamopMebia arcJiidona it is exactly reversed, the tip 

 of the anterior wing (Fig. 14) is prolonged, and forms the stalk, while 

 a broad, dark, stripe, the midrib (mr), runs from there across the 

 middle of both wings, and seems to give off" two or three lateral ribs 

 running outwards. If it be asked whether this butterfly always sits 

 i. a 



Fig. 14. CamopMebia archidona, from Bolivia, in its 

 resting attitude, mr, midrib of the apparent leaf. 

 st, the apparent stalk. 



