362 TROPICAL NATURE 



protective, serving as a warning of their uneatableness. 1 On 

 our theory none of these colours offer any difficulty. Con- 

 spicuousness being useful, every variation tending to brighter 

 and purer colours was selected ; the result being the beautiful 

 variety and contrast we find. 



Imitative Warning Colours the Theory of Mimicry 

 We now come to those groups which gain protection solely 

 by being mistaken for some of these brilliantly coloured but 

 uneatable creatures, and here a difficulty really exists, and to 

 many minds is so great as to be insuperable. It will be well 

 therefore to endeavour to explain how the resemblance in 

 question may have been brought about. 



The most difficult case, and the one which may be taken 

 as a type of the whole class, is that of the genus Leptalis (a 

 group of South American butterflies allied to our common 

 white and yellow kinds), many of the larger species of which 

 are still white or yelloAv, and which are all eatable by birds 

 and other insectivorous creatures. But there are also a 

 number of species of Leptalis, which are brilliantly red, 

 yellow, and black, and which, band for band and spot for 

 spot, resemble some one of the Danaidse or Heliconidae which 

 inhabit the same district and which are nauseous and uneat- 

 able. Now the usual difficulty is, that a slight approach to 

 one of these protected butterflies would be of no use, while a 

 greater sudden variation is not admissible on the theory of 

 gradual change by indefinite slight variations. This objection 

 depends almost wholly on the supposition that, when the first 

 steps towards mimicry occurred, the South American Danaidse 

 were what they are now ; while the ancestors of the Leptalides 

 were like the ordinary white or yellow Pieridse to which they 

 are allied. But the Danaioid butterflies of South America are 

 so immensely numerous and so greatly varied, not only in colour 

 but in structure, that we may be sure they are of vast antiquity 

 and have undergone great modification. A large number of 

 them, however, are still of comparatively plain colours, often 

 rendered extremely elegant by the delicate transparency of 

 the wing membrane, but otherwise not at all conspicuous. 



1 This has since been found to be the case by Professor Herdman (Trans. 

 Biol. Soc. Liverpool, vol. iv. p. 150). 



