RESEMBLANCES AMONG ANIMALS. 85 



to the Heliconida3, and that it is therefore equally an 

 advantage to other insects to be mistaken for them. 



O 



There is also another extraordinary fact that we are 

 not yet in a position clearly to comprehend : some 

 groups of the Heliconida3 themselves mimic other 

 groups. Species of Heliconia mimic Mechanitis, and 

 every species of Napeogenes mimics some other Heli- 

 conideous butterfly. This would seem to indicate that 

 the distasteful secretion is not produced alike by all 

 members of the family, and that where it is deficient 

 protective imitation comes into play. It is this, per- 

 haps, that has caused such a general resemblance 

 among the HeliconidaB, such a uniformity of type with 

 great diversity of colouring, since any aberration 

 causing an insect to cease to look like one of the family 

 would inevitably lead to its being attacked, wounded, 

 and exterminated, even although it was not eatable. 

 In other parts of the world an exactly parallel series 

 of facts have been observed. The Danaidas and the 

 Acrseidse of the Old World tropics form in fact one 

 great group with the HeliconidaB. They have the same 

 general form, structure, -and habits: they possess the 

 same protective odour, and are equally abundant in 

 individuals, although not so varied in colour, blue and 

 white spots on a black ground being the most general 

 pattern. The insects which mimic these are chiefly 

 Papilios, and Diadema, a genus allied to our peacock 

 and tortoiseshell butterflies. In tropical Africa there is 

 a peculiar group of the genus Danais, characterized 

 by dark-brown and bluish-white colours, arranged in 



