The head and antennae are drawn back between the wings so as to be quite concealed, and there is a little notch hollowed out at the very base of the wings, which allows the head to be retracted sufficiently.

All these varied details combine to produce a disguise that is so complete and marvellous as to astonish everyone who observes it; and the habits of the insects are such as to utilize all these peculiarities, and render them available in such a manner as to remove all doubt of the purpose of this singular case of mimicry, which is undoubtedly a protection to the insect.
Its strong and swift flight is sufficient to save it from its enemies when on the wing, but if it were equally conspicuous when at rest it could not long escape extinction, owing to the attacks of the insectivorous birds and reptiles that abound in the tropical forests.

A very closely allied species, Kallima inachis, inhabits India, where it is very common, and specimens are sent in every collection from the Himalayas.

On examining a number of these, it will be seen that no two are alike, but all the variations correspond to those of dead leaves.
Every tint of yellow, ash, brown, and red is found here, and in many specimens there occur patches and spots formed of small black dots, so closely resembling the way in which minute fungi grow on leaves that it is almost impossible at first not to believe that fungi have grown on the butterflies themselves! If such an extraordinary adaptation as this stood alone, it would be very difficult to offer any explanation of it; but although it is perhaps the most perfect case of protective imitation known, there are hundreds of similar resemblances in nature, and from these it is possible to deduce a general theory of the manner in which they have been slowly brought about.

The principle of variation and that of "natural selection," or survival of the fittest, as elaborated by Mr.
Darwin in his celebrated "Origin of Species," offers the foundation for such a theory; and I have myself endeavoured to apply it to all the chief cases of imitation in an article published in the "Westminster Review" for 1867, entitled, "Mimicry, and other Protective Resemblances Among Animals," to which any reader is referred who wishes to know more about this subject.
In Sumatra, monkeys are very abundant, and at Lobo Kaman they used to frequent the trees which overhang the guard-house, and give me a fine opportunity of observing their gambols.