l80 THE DOCTRINE OF DESCENT. 



ordinarily extensive; they are remarkable for their 

 elongated wings, body, and antennae, and for the beauty 

 of their colours. It might be imagined they were 

 exposed to the persecutions of insectivorous birds and 

 other animals ; hut this is not the case, for they have a 

 disagreeable smell, which, in all likelihood, renders them 

 obnoxious. Their smell and flavour are thus a protection, 

 as the birds and lizards who have once seized them by 

 mistake are certain, ever after, to leave them unmolested. 

 Now, as the insectivora do not test the individual case, 

 but have adopted a general repugnance to the aspect of 

 the Heliconidae, if other butterflies resembled the Heli- 

 conidae without possessing the bad smell, they would 

 participate in the security to life enjoyed by the Heli- 

 conidae in proportion as they approach their external 

 appearance. This case has actually occurred, for Bates 

 discovered a number of species of the otherwise very 

 different genus, Leptalis, of which each almost undis- 

 tinguishably resembles one of the Heliconidae both in 

 colour and form. The Leptalidae have also adopted the 

 flight of the Heliconidae, share their habitats, and, 

 although without the offensive smell, fly about with 

 impunity. This state of things would be impossible if 

 the Leptalidae were not considerably in the minority, so 

 as to be in a measure hidden by the Heliconidae. 



Wallace has proved that species protected by mimicry 

 of other animals are invariably in the minority, and 

 often very rare in comparison with the species which 

 they imitate. Neither the explanation that like condi- 

 tions of life produced like results, nor the hypothesis 

 that, in some cases at least, the mimiciy consists in 

 reversion to a common original species, is in any way 



