14 ANIMAL COLORATION. 



The Action of Natural Selection in producing Colour Changes must 

 be strictly Limited. 



AlthougJi it is reasonable to suppose that tlie elimination of 

 unfit varieties may in some cases have led to the perfecting 

 of say a colour resembla.iice between the underside of a butter- 

 fly's wing and a decaying leaf, calculated to deceive its enemies, 

 such action must be limited in various ways. The material 

 with which natural selection has to work is often very 

 restricted. One kind of modification may be possible in one 

 group which is quite impossible in another. Certain genera 

 of " Whites," such as Leptalis, are believed to owe their 

 striking resemblance to certain species of another family of 

 butterflies — the Heliconidas — to a need for protection : the 

 Heliconidse are distasteful to insect-eating birds, monkeys^ 

 and other animals ; in consequence, they enjoy an immunity 

 from the attacks of these animals. 



This immunity is apparently shared by Lejptalis on account 

 of its being mistaken for a Heliconid. It has the same shaped 

 wings and the same pattern of coloration. Now, this shape 

 and pattern are unusual among the " Whites," but it must be 

 remembered that the actual colours are present : yellow, white,, 

 black and red are found among members of the family Pieridje 

 which bear no resemblance to the Heliconidte ; the shape of 

 the wings, too, which is so characteristic of the Heliconidas is 

 met with in at least one white butterfly — the Wood White. It 

 is, therefore, not so remarkable to find the striking resemblance 

 that exists between certain Pieridte and certain Heliconida? ; 

 the impression that is given by some books dealing with such 

 subjects is that the mimicking Pierids have, so to speak-, gone 

 a very long way out of their road in assuming the livery of the 

 Heliconidae. A mimicry between one of the " Blues " and a 



