onidae, 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 Heliconidae themselves mimic other groups. Species of
Heliconia mimic Mechanitis, and every species of Napeogenes mimics some
other Heliconideous 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, perhaps, that has caused such a general resemblance
among the Heliconidae, 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 Danaidae and the Acraeidae of the Old World tropics form
in fact one great group with the Heliconidae. 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 bands or stripes. One
of these, Danais niavius, is exactly imitated both by Papilio hippocoon
and by Diadema anthedon; another, Danais echeria, by Papilio cenea; and
in Natal a variety of the Danais is found having a white spot at the tip
of wings, accompanied by a variety of the Papilio bearing a
corresponding white spot. Acraea gea is copied in its very peculiar style
of colouration by the female of Papilio cynorta, by Panopaea hirce, and
by the female of Elymnias phegea. Acraea euryta of Calabar has a female
variety of Panopea hirce from the same place which exactly copies it;
and Mr. Trimen, in his paper on Mimetic Analogies among African
Butterflies, published in the Transactions of the Linnaean Society for
1868, gives a list of no less than sixteen species and varieties of
Diadema and its allies, and ten of Papilio, which in their colour and
markings are perfect mimics o