RESEMBLANCES AMONG ANIMALS. 85 
to the Heliconide, and that it is therefore equally an 
advantage to other insects to be mistaken for them. 
There is also another extraordinary fact that we are 
not yet in a position clearly to comprehend: some 
groups of the Heliconide 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 Heliconidz, 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 Danaide and the 
Acreide of the Old World tropics form in fact one 
great group with the Heliconide. 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 
