DARWIN 19 



usually resemble the males (or are equally brightly coloured) 

 shows that the usual tendency is to transmit colour to both 

 sexes when it is not injurious to either. 



" Now for the special argument. 



" 6. In the very weak-flying Leptalis both sexes mimic 

 Heliconidae. But in the much stronger flying — Papilio, Pieris, 

 and Diadema — it is the female only that mimics the protected 

 group, and in these cases the females often acquire brighter 

 and more conspicuous colours than the male. 



" 7. No case is known of a male Papilio, Pieris, or Diadema, 

 alone, mimicking a protected species ; yet colour is more fre- 

 quent in males, and variations are always ready for the pur- 

 pose of sexual or other forms of selection. 



" 8. The fair inference seems to be that each species, and 

 also each sex, can only be modified by selection just as far 

 as is absolutely necessary — not a step further. A male, being 

 by structure and habits less exposed to danger, and therefore 

 requiring less protection than the female, cannot have an equal 

 amount of protection given to it by natural selection; but the 

 female must have some extra protection to balance her greater 

 exposure to danger, and she rapidly acquires it in one way or 

 another. 



"9. The objection as to male fish, which seem to require 

 protection, yet have sometimes bright colours, seems to me 

 of no more weight than is the existence of some unprotected 

 species of white Leptalis as a disproof of Bates's theory of 

 mimicry, — or that only a few species of butterfly resemble 

 leaves, — or that the habits and instincts that protect one animal 

 are absent in allied species. These are all illustrations of the 

 many and varied ways in which nature works to give the exact 

 amount of protection it needs to each species." 



3. Arctic Plants in the Southern Hemisphere, and on 

 Isolated Mountain-tops within the Tropics. — Having paid 

 great attention to the whole question of the distribution of 

 organisms, I was obliged to reject Mr. Darwin's explanation 

 of the above phenomena by a cooling of the tropical lowlands 

 of the whole earth during the glacial period to such an extent 



