of such successful masquerading will perhaps best serve to introduce the general principles upon which all animal mimicry ultimately depends. Indeed, naturalists of late years have been largely employed in fishing up examples from the ends of the earth and from the depths of the sea for the elucidation of this very subject. There is a certain butterfly in the islands of the Malay Archipelago (its learned name, if anybody wishes to be formally introduced, is Kallima paralekta) which always rests among dead or dry leaves, and has itself leaf-like wings, all spotted over at intervals with wee speckles to imitate the tiny spots of fungi on the foliage it resembles. The well-known stick and leaf insects from the same rich neighbourhood in like manner exactly mimic the twigs and leaves of the forest among which they lurk: some of them look for all the world like little bits of walking bamboo, while others appear in all varieties of hue, as if opening buds and full-blown leaves and pieces of yellow foliage sprinkled with the tints and moulds of decay had of a sudden raised themselves erect upon six legs, and begun incontinently to perambulate the Malayan woodlands like vegetable Frankensteins in all their glory. The larva of one such deceptive insect, observed in Nicaragua by sharp-eyed Mr. Belt, appeared at first sight like a mere fragment of the moss on which it rested, its body being all prolonged into little thread-like green filaments, precisely imitating the foliage around it. Once more, there are common flies which secure protection for themselves by growing into the counterfeit presentment of wasps or hornets, and so obtaining immunity from the attacks of birds or animals. Many of these curiously mimetic insects are banded with yellow and black in the very image of their stinging originals, and have their tails sharpened, in terrorem, into a pretended sting, to give point and verisimilitude to the deceptive resemblance. More curious still, certain South American butterflies of a perfectly inoffensive and edible family mimic in every spot and line of colour sundry other butterflies of an utterly unrelated and fundamentally dissimilar type, but of so disagreeable a taste as never to be eaten by birds or lizards. The origin of these curious resemblances I shall endeavour to explain (after Messrs. Bates and Wallace) a little farther on: for the present it is enough to observe that the extraordinary resemblances thus produced have often deceived the very elect, and have caused experienced naturalists for a time to stick some deceptive specimen of a fly among the wasps and hornets, or some masquerading cricket into the midst of a cabinet full of saw-flies or ichneumons.
Let us look briefly at the other instances of protective coloration in nature generally which lead up to these final bizarre exemplifications of the masquerading tendency.
Wherever all the world around is remarkably uniform in colour and appearance, all the animals, birds, and insects alike necessarily disguise themselves in its prevailing tint to escape observation. It does not matter in the least whether they are predatory or defenceless, the hunters or the hunted: if they are to escape destruction or starvation, as the case may be, they must assume the hue of all the rest of nature about them. In the arctic snows, for example, all animals, without exception, must needs be snow-white. The polar bear, if he were brown or black, would immediately be observed among the unvaried ice-fields by his expected prey, and could never get a chance of approaching his quarry unperceived at close quarters. On the other hand, the arctic hare must equally be dressed in a snow-white coat, or the arctic fox would too readily discover him and pounce down upon him off-hand; while, conversely, the fox himself, if red or brown, could never creep upon the unwary hare without previous detection, which would defeat his purpose. For this reason, the ptarmigan and the willow grouse become as white in winter as the vast snow-fields under which they burrow; the ermine changes his dusky summer coat for the expensive wintry suit beloved of British Themis; the snow-bunting acquires his milk-white plumage; and even the weasel assimilates himself more or less in hue to the unvarying garb of arctic nature. To be out of the fashion is there quite literally to be out of the world: no half-measures will suit the stern decree of polar biology; strict compliance with the law of winter change is absolutely necessary to success in the struggle for existence.
Now, how has this curious uniformity of dress in arctic animals been brought about? Why, simply by that unyielding principle of Nature which condemns the less adapted for ever to extinction, and exalts the better adapted to the high places of her hierarchy in their stead. The ptarmigan and the snow-buntings that look most like the snow have for ages been least likely to attract the unfavourable attention of arctic fox or prowling ermine; the fox or ermine that came most silently and most unperceived across the shifting drifts has been most likely to steal unawares upon the heedless flocks of ptarmigan and snow-bunting. In the one case protective colouring preserves the animal from himself being devoured; in the other case it enables him the more easily to devour others. And since 'Eat or be eaten' is the shrill sentence of Nature upon all animal life, the final result is the unbroken whiteness of the arctic fauna in all its developments of fur or feather.
Where the colouring of nature is absolutely uniform, as among the arctic snows or the chilly mountain tops, the colouring of the animals is uniform too. Where it is slightly diversified from point to point, as in the sands of the desert, the animals that imitate it are speckled or diversified with various soft neutral tints. All the birds, reptiles, and insects of Sahara, says Canon Tristram, copy closely the grey or isabelline colour of the boundless sands that stretch around them. Lord George Campbell, in his amusing 'Log Letters from the "Challenger,"' mentions a butterfly on the shore at Amboyna which looked exactly like a bit of the beach, until it spread its wings and fluttered away gaily to leeward. Soles and other flat-fish similarly resemble the sands or banks on which they lie, and accommodate themselves specifically to the particular colour of their special bottom. Thus the flounder imitates the muddy bars at the mouths of rivers, where he loves to half bury himself in the congenial ooze; the sole, who rather affects clean hard sand-banks, is simply sandy and speckled with grey; the plaice, who goes in by preference for a bed of mixed pebbles, has red and yellow spots scattered up and down irregularly among the brown, to look as much as possible like agates and carnelians: the brill, who hugs a still rougher ledge, has gone so far as to acquire raised lumps or tubercles on his upper surface, which make him seem like a mere bit of the shingle-strewn rock on which he reposes. In short, where the environment is most uniform the colouring follows suit: just in proportion as the environment varies from place to place, the colouring must vary in order to simulate it. There is a deep biological joy in the term 'environment'; it almost rivals the well-known consolatory properties of that sweet word 'Mesopotamia.' 'Surroundings,' perhaps, would equally well express the meaning, but then, as Mr. Wordsworth justly observes, 'the difference to me!'
Between England and the West Indies, about the time when one begins to recover from the first bout of sea-sickness, we come upon a certain sluggish tract of ocean, uninvaded by either Gulf Stream or arctic current, but slowly stagnating in a sort of endless eddy of its own, and known to sailors and books of physical geography as the Sargasso Sea. The sargasso or floating seaweed from which it takes its poetical name is a pretty yellow rootless alga, swimming in vast quantities on the surface of the water, and covered with tiny bladder-like bodies which at first sight might easily be mistaken for amber berries. If you drop a bucket over the ship's side and pull up a tangled mass of this beautiful seaweed, it will seem at first to be all plant alike; but, when you come to examine its tangles closely, you will find that it simply swarms with tiny crabs, fishes, and shrimps, all coloured so precisely to shade that they look exactly like the sargasso itself. Here the colour about is less uniform than in the arctic snows, but, so far as the sargasso-haunting animals are concerned, it comes pretty much to the same thing. The floating mass of weed is their whole world, and they have had to accommodate themselves to its tawny hue under pain of death, immediate and violent.
Caterpillars and butterflies often show us a further step in advance in the direction of minute imitation of ordinary surroundings. Dr. Weismann has published a very long and learned memoir, fraught with the best German erudition and prolixity, upon this highly interesting and obscure subject. As English readers, however, not unnaturally object to trudging through a stout volume on the larva of the sphinx moth, conceived in the spirit of those patriarchal ages of Hilpa and Shalum, when man lived to nine hundred and ninety-nine years, and devoted a stray century or so without stint to the work of education, I shall not refer them to Dr. Weismann's original treatise, as well translated and still further enlarged by Mr. Raphael Meldola, but
