from dusky through pinkish to pale green. It is interesting to note, that the colours produced were in all cases such only as assimilated with the surroundings usually occupied by the species, and also, that colours which did not occur in such surroundings, as dark red or blue, only produced the same effects as dusky or black.

Careful experiments were made to ascertain whether the effect was produced through the sight of the caterpillar. The ocelli were covered with black varnish, but neither this, nor cutting off the spines of the tortoise-shell larva to ascertain whether they might be sense-organs, produced any effect on the resulting colour. Mr. Poulton concludes, therefore, that the colour-action probably occurs over the whole surface of the body, setting up physiological processes which result in the corresponding colour-change of the pupa. Such changes are, however, by no means universal, or even common, in protectively coloured pupa, since in Papilio machaon and some others which have been experimented on, both in this country and abroad, no change can be produced on the pupa by any amount of exposure to differently coloured surroundings. It is a curious point that, with the small tortoise-shell larva, exposure to light from gilded surfaces produced pupæ with a brilliant golden lustre; and the explanation is supposed to be that mica abounded in the original habitat of the species, and that the pupa thus obtained protection when suspended against micaceous rock. Looking, however, at the wide range of the species and the comparatively limited area in which micaceous rocks occur, this seems a rather improbable explanation, and the occurrence of this metallic appearance is still a difficulty. It does not, however, commonly occur in this country in a natural state.

The two classes of variable colouring here discussed are evidently exceptional, and can have little if any relation to the colours of those more active creatures which are continually changing their position with regard to surrounding objects, and whose colours and markings are nearly constant throughout the life of the individual, and (with the exception of sexual differences) in all the individuals of the species. We will now briefly pass in review the various characteristics and uses of the colours which more generally prevail in nature;

and having already discussed those protective colours which serve to harmonise animals with their general environment, we have to consider only those cases in which the colour resemblance is more local or special in its character.

Special or Local Colour Adaptations.

This form of colour adaptation is generally manifested by markings rather than by colour alone, and is extremely prevalent both among insects and vertebrates, so that we shall be able to notice only a few illustrative cases. Among our native birds we have the snipe and woodcock, whose markings and tints strikingly accord with the dead marsh vegetation among which they live; the ptarmigan in its summer dress is mottled and tinted exactly like the lichens which cover the stones of the higher mountains; while young unfledged plovers are spotted so as exactly to resemble the beach pebbles among which they crouch for protection, as beautifully exhibited in one of the cases of British birds in the Natural History Museum at South Kensington.

In mammalia, we notice the frequency of rounded spots on forest or tree haunting animals of large size, as the forest deer and the forest cats; while those that frequent reedy or grassy places are striped vertically, as the marsh antelopes and the tiger. I had long been of opinion that the brilliant yellow and black stripes of the tiger were adaptive, but have only recently obtained proof that it is so. An experienced tiger-hunter, Major Walford, states in a letter, that the haunts of the tiger are invariably full of the long grass, dry and pale yellow for at least nine months of the year, which covers the ground wherever there is water in the rainy season, and he adds: "I once, while following up a wounded tiger, failed for at least a minute to see him under a tree in grass at a distance of about twenty yards-jungle open-but the natives saw him, and I eventually made him out well enough to shoot him, but even then I could not see at what part of him I was aiming. There can be no doubt whatever that the colour of both the tiger and the panther renders them almost invisible, especially in a strong blaze of light, when among grass, and one does not seem to notice stripes or spots till they are dead." It is the black shadows of the vegetation that

assimilate with the black stripes of the tiger; and, in like manner, the spotty shadows of leaves in the forest so harmonise with the spots of ocelots, jaguars, tiger-cats, and spotted deer as to afford them a very perfect concealment.

In some cases the concealment is effected by colours and markings which are so striking and peculiar that no one who had not seen the creature in its native haunts would imagine them to be protective. An example of this is afforded by the banded fruit pigeon of Timor, whose pure white head and neck, black wings and back, yellow belly, and deeply-curved black band across the breast, render it a very handsome and conspicuous bird. Yet this is what Mr. H. O. Forbes says of it "On the trees the white-headed fruit pigeon (Ptilopus cinctus) sate motionless during the heat of the day in numbers, on well-exposed branches; but it was with the utmost difficulty that I or my sharp-eyed native servant could ever detect them, even in trees where we knew they were sitting.' The trees referred to are species of Eucalyptus which abound in Timor. They have whitish or yellowish bark and very open foliage, and it is the intense sunlight casting black curved shadows of one branch upon another, with the white and yellow bark and deep blue sky seen through openings of the foliage, that produces the peculiar combination of colours and shadows to which the colours and markings of this bird have become so closely assimilated.

Even such brilliant and gorgeously coloured birds as the sun-birds of Africa are, according to an excellent observer, often protectively coloured. Mrs. M. E. Barber remarks that "A casual observer would scarcely imagine that the highly varnished and magnificently coloured plumage of the various species of Nectarinia could be of service to them, yet this is undoubtedly the case. The most unguarded moments of the lives of these birds are those that are spent amongst the flowers, and it is then that they are less wary than at any other time. The different species of aloes, which blossom in succession, form the principal sources of their winter supplies of food; and a legion of other gay flowering plants in spring and summer, the aloe blossoms especially, are all brilliantly coloured, and they harmonise admirably with the gay plumage 1 A Naturalist's Wanderings in the Eastern Archipelago, p. 460.

Even the keen eye of a

of the different species of sun-birds. hawk will fail to detect them, so closely do they resemble the flowers they frequent. The sun-birds are fully aware of this fact, for no sooner have they relinquished the flowers than they become exceedingly wary and rapid in flight, darting arrowlike through the air and seldom remaining in exposed situations. The black sun-bird (Nectarinia amethystina) is never absent from that magnificent forest-tree, the 'Kaffir Boom' (Erythrina caffra); all day long the cheerful notes of these birds may be heard amongst its spreading branches, yet the general aspect of the tree, which consists of a huge mass of scarlet and purpleblack blossoms without a single green leaf, blends and harmonises with the colours of the black sun-bird to such an extent that a dozen of them may be feeding amongst its blossoms without being conspicuous, or even visible." 1

Some other cases will still further illustrate how the colours of even very conspicuous animals may be adapted to their peculiar haunts.

The late Mr. Swinhoe says of the Kerivoula picta, which he observed in Formosa: "The body of this bat was of an orange colour, but the wings were painted with orange-yellow and black. It was caught suspended, head downwards, on a cluster of the fruit of the longan tree (Nephelium longanum). Now this tree is an evergreen, and all the year round some portion of its foliage is undergoing decay, the particular leaves being, in such a stage, partially orange and black. This bat can, therefore, at all seasons suspend from its branches and elude its enemies by its resemblance to the leaves of the tree."2

Even more curious is the case of the sloths-defenceless animals which feed upon leaves, and hang from the branches of trees with their back downwards. Most of the species have a curious buff-coloured spot on the back, rounded or oval in shape and often with a darker border, which seems placed there on purpose to make them conspicuous; and this was a great puzzle to naturalists, because the long coarse gray or greenish hair was evidently like tree-moss and therefore protective. But an old writer, Baron von Slack, in his Voyage 1 Trans. Phil. Soc. (? of S. Africa), 1878, part iv, 2 Proc. Zool. Soc., 1862 p. 357.

p. 27.

He

to Surinam (1810), had already explained the matter. says: "The colour and even the shape of the hair are much like withered moss, and serve to hide the animal in the trees, but particularly when it has that orange-coloured spot between the shoulders and lies close to the tree; it looks then exactly like a piece of branch where the rest has been broken off, by which the hunters are often deceived." Even such a huge animal as the giraffe is said to be perfectly concealed by its colour and form when standing among the dead and broken trees that so often occur on the outskirts of the thickets where it feeds. The large blotch-like spots on the skin and the strange shape of the head and horns, like broken branches, so tend to its concealment that even the keen-eyed natives have been known to mistake trees for giraffes or giraffes for trees.

Innumerable examples of this kind of protective colouring occur among insects; beetles mottled like the bark of trees or resembling the sand or rock or moss on which they live, with green caterpillars of the exact general tints of the foliage they feed on; but there are also many cases of detailed imitation of particular objects by insects that must be briefly described.1

Protective Imitation of Particular Objects.

The insects which present this kind of imitation most perfectly are the Phasmidæ, or stick and leaf insects. The well

1 With reference to this general resemblance of insects to their environment the following remarks by Mr. Poulton are very instructive. He says: "Holding the larva of Sphinx ligustri in one hand and a twig of its foodplant in the other, the wonder we feel is, not at the resemblance but at the difference; we are surprised at the difficulty experienced in detecting so conspicuous an object. And yet the protection is very real, for the larvæ will be passed over by those who are not accustomed to their appearance, although the searcher may be told of the presence of a large caterpillar. An experienced entomologist may also fail to find the larvæ till after a considerable search. This is general protective resemblance, and it depends upon a general harmony between the appearance of the organism and its whole environment. It is impossible to understand the force of this protection for any larva, without seeing it on its food-plant and in an entirely normal condition. The artistic effect of green foliage is more complex than we often imagine; numberless modifications are wrought by varied lights and shadows upon colours which are in themselves far from uniform. In the larva of Papilio machaon the protection is very real when the larva is on the food-plant, and can hardly be appreciated at all when the two are apart." Numerous other examples are given in the chapter on Mimicry and other Protective Resemblances among Animals," in my Contributions to the Theory of Natural Selection.

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