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NYONE of an observant turn of mind who has the good fortune to live in the country, or who walks with a critical eye through the galleries of a wellappointed museum of natural history, will be struck by the fact that the colours and shapes of the animals exhibited are mostly of two kinds. In one case they are adapted so as to render their possessor invisible; in the other they serve exactly the opposite purpose, and render it conspicuous. The reason for the first is perfectly clear, and has been understood since the earliest days of zoology. The discovery of the significance of the second is, however, of comparatively recent date, and has opened one of the most attractive chapters in the history of animal life.

The colours or other attributes which make an animal conspicuous are now known to act as a danger-signal, warning enemies to keep at a distance; hence they have been very appropriately called "warning" characters. They are primarily distinctive of animals which are either dangerous to meddle with or disagreeable. to taste; but they are almost as commonly found in others that are harmless and tasty, and mimic the poisonous or nauseous species for purposes of protection.

A good illustration of warning colouring is supplied by the common North American skunk (Fig. 1). This animal is of the badger kind, and is about as large as a small cat, but has shorter, stumpier legs, a No. 187. April 1899

long thick coat, and a long bushy tail. He is jet black in colour, with a whitish tail and nearly snow-white bands along the back and sides. Timidity, caution, and a sneaking gait stamp the behaviour of most wild animals of this size: but not the skunk. With an easy jogging trot, he comes along the middle of the road, not in a skulking fashion, every sense alert to warn him of danger, but in a leisurely, dauntless manner, turning aside for no one, flaunting in the air as a danger-signal his great black and white tail, and warning all and sundry to keep aloof.

What is the meaning of this fearlessness in a creature to all appearance so defenceless? Yes, to all appearance defenceless, but in reality very much the opposite. For his size the skunk is certainly one of the most terrible creatures in the world to tackle at close quarters; so terrible a customer indeed, that few animals, even though far surpassing him in size and strength, will venture to attack him—at least not a second time. Were it merely a matter of claws and teeth, any well-trained fox-terrier dog would shake the life out of him in ten seconds. But the skunk relies upon other weapons; he is protected by a deadly artillery in the form of a fœtid liquid, which is discharged from beneath the tail in the face of the advancing foe. This liquid burns like sulphuric acid; a drop in the eye causes blindness. A passing whiff of the smell reminds one of the

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concentrated essence of the odour of ferrets increased a hundredfold, with a flavour of fox thrown in; and weeks of washing will fail to eradicate the stench of it from one's clothes.

This is the reason for the air of absolute unconcern with which the skunk goes about his business. He has no fear; he wishes to be seen and recognised by all, and he is splendidly marked with white that he may be visible in the dusk, and so escape the risk of being mistaken for a harmless creature by enemies lying in wait for prey. He has no wish to be attacked. He might be bowled over, grievously damaged, or even killed outright before his assailant discovered his mistake. So to avoid such a contingency he makes himself as conspicuous as possible, not, of course, from any altruistic intention of saving his foe from a disagreeable experience, but for the purely selfish motive of being allowed to go his own way without let or hindrance.

It is exactly the same with butterflies, moths, and other insects provided with acrid juices that make them distasteful. Those that possess no such means of defence are either swift, strong fliers, and when on the wing hurry along in terror of pursuit, or are so coloured above and below that they vanish from view upon alighting. But the nauseous species are weak of wing and flap slowly about in broad daylight, without hurry and without fear, displaying their gaudy colours in the brilliant sunshine and courting the notice of insect-eaters. Boldness, abundance and strongly contrasted patterns of yellow and black, black and red, or black and white are the distinguishing features of nearly all insects and animals akin to them that are either distasteful or venomous.

The three Indian moths (Euschema militaris, Eusemia maculatrix, and Milionia Pyrozonis) depicted on our coloured plate may be taken as instances of the prevailing colours of nauseous species; and bees and wasps, with their livery of black and yellow, are familiar examples belonging to the category of venomous species.

It has long been known that animals that are protected from attack by possessing any of the attributes mentioned above, such as poison glands, or a disagreeable. taste or odour, are imitated both in colour and form, and often in little tricks of manner, by other harmless and edible kinds. The latter by this means conceal their identity from their foes, and so escape destruction. This is the phenomenon that is called "mimicry.”

It is, perhaps, unfortunate that, as ordinarily understood, the word "mimicry" carries with it the idea of conscious or voluntary action, because consciousness and volition have no influence whatever, so far as is known, in producing or fostering the resemblances in question. They have been brought about, it is believed, by the process which Darwin called "natural selection." A simple illustration will make this clear. Suppose that in a certain locality there is a race of nauseous butterflies coloured black and white, and another race of edible butterflies adorned with different tints. Creatures that feed upon butterflies—and there are many that do-will start by killing both sorts; but after one or two experiments they will learn that the blackand-white kind are not worth the trouble of catching, and will, naturally enough, leave them in peace and turn the whole of their attention to the tasty ones. Now, it is clear that if any of the latter vary in colour in the direction of the nauseous race and all members of a race vary more or less-they will have a much greater chance of surviving to propagate the resemblance than those that adhere to the original tints of their kind. But the progeny of the survivors will also vary, some resembling the protected. species more than their parents do,