510 MR. H. W 
I think it will be conceded that all these various kinds of imitative resemblances belong 
to the same class of phenomena, and are subject to the same explanation. The fact of 
one species mimicking an inanimate object, and another of an allied genus a living 
insect of another family, sufficiently proves this. I do not see how they differ from the 
adaptations of organs or instincts to the functions or objects they relate to. All are 
adaptations, either of the whole outward dress or of special parts, having in view the 
welfare of the creatures that possess them. 
Every species in nature may be looked upon as maintaining its existence by virtue of 
some endowment enabling it to withstand the host of adverse circumstances by which 
it is surrounded. The means are of endless diversity. Some are provided with special 
organs of offence, others have passive means of holding their own in the battle of life. 
Great fecundity is generally of much avail, added to capabilities, active or passive, of 
wide dispersion ; so that when the species is extirpated in one part of its area of distribu- 
tion, the place is refilled by migration of individuals from another part. A great number 
have means of concealment from their enemies, of one sort or other. Many are enabled 
to escape extermination, or obtain subsistence, by disguises of various kinds : amongst 
these must be reckoned the adaptive resemblance of an otherwise defenceless species to 
one whose flourishing race shows that it enjoys peculiar advantages. 
"What advantages the Heliconidce possess to make them so flourishing a group, and 
consequently the objects of so much mimetic resemblance, it is not easy to discover. 
There is nothing apparent in their structure or habits which could render them safe 
from persecution by the numerous insectivorous animals which are constantly on the 
watch in the same parts of the forest which they inhabit. It is probable they are un- 
palatable to insect enemies. Some of them (Jjycorea, Ituna) have exsertible glands near the 
anus, which are protruded when the insects are roughly handled ; it is well known that 
similar organs in other families ( Carabidce, Staphylinidce) secrete fetid liquids or gases, 
and serve as a protection to the species. I have noticed also that recently killed speci- 
mens of Danaoid Heliconidce, when set out to dry, were always less subject than other 
insects to be devoured by vermin. They have all a peculiar smell*. I never saw the 
flocks of slow-flying Heliconidce in the woods persecuted by birds or Dragon-flies, to 
which they would have been easy prey ; nor, when at rest on leaves, did they appear to 
be molested by Lizards or the predacious Plies of the family Asilidce, which were very 
» 
often seen pouncing on Butterflies of other families. If they owe their flourishing ex- 
istence to this cause, it would be intelligible why the Leptalidce, whose scanty number 
of individuals reveals a less protected condition, should be disguised in their dress, and 
thus share their immunity. 
This explanation, however, would not apply to the imitation of Danaoid Heliconidce 
by other species of the same subfamily. Moreover, there are several genera of other 
groups (e. g., Heliconius, JPapiHo) which contain mimetic species side by side with species 
that are the objects of mimicry by members of other families, as will be seen by reference 
to the Table at p. 503. There is no reason to conclude that some of these possess the 
peculiar means of defence of the Danaoid Heliconidce, whilst their near kindred are de- 
* Mr. Wallace tells me the Euplcea of the Eastern Archipelago have also this peculiar smell. 
