I have left to the last the most marvellous cases of mimicry of all—those noticed among South American butterflies by Mr. Bates, who found that certain edible kinds exactly resembled a handsome and conspicuous but bitter-tasted species 'in every shade and stripe of colour.' Several of these South American imitative insects long deceived the very entomologists; and it was only by a close inspection of their structural differences that the utter distinctness of the mimickers and the mimicked was satisfactorily settled. Scarcely less curious is the case of Mr. Wallace's Malayan orioles, two species of which exactly copy two pugnacious honey-suckers in every detail of plumage and coloration. As the honey-suckers are avoided by birds of prey, owing to their surprising strength and pugnacity, the orioles gain immunity from attack by their close resemblance to the protected species. When Dr. Sclater, the distinguished ornithologist, was examining Mr. Forbes's collections from Timorlaut, even his experienced eye was so taken in by another of these deceptive bird-mimicries that he classified two birds of totally distinct families as two different individuals of the same species.
Even among plants a few instances of true mimicry have been observed. In the stony African Karoo, where every plant is eagerly sought out for food by the scanty local fauna, there are tubers which exactly resemble the pebbles around them; and I have little doubt that our perfectly harmless English dead-nettle secures itself from the attacks of browsing animals by its close likeness to the wholly unrelated, but well-protected, stinging-nettle.
Finally, we must not forget the device of those animals which not merely assimilate themselves in colour to the ordinary environment in a general way, but have also the power of adapting themselves at will to whatever object they may happen to lie against. Cases like that of the ptarmigan, which in summer harmonises with the brown heather and grey rock, while in winter it changes to the white of the snow-fields, lead us up gradually to such ultimate results of the masquerading tendency. There is a tiny crustacean, the chameleon shrimp, which can alter its hue to that of any material on which it happens to rest. On a sandy bottom it appears grey or sand-coloured; when lurking among seaweed it becomes green, or red, or brown, according to the nature of its momentary background. Probably the effect is quite unconscious, or at least involuntary, like blushing with ourselves—and nobody ever blushes on purpose, though they do say a distinguished poet once complained that an eminent actor did not follow his stage directions because he omitted to obey the rubrical remark, 'Here Harold purples with anger.' The change is produced by certain automatic muscles which force up particular pigment cells above the others, green coming to the top on a green surface, red on a ruddy one, and brown or grey where the circumstances demand them. Many kinds of fish similarly alter their colour to suit their background by forcing forward or backward certain special pigment-cells known as chromatophores, whose various combinations produce at will almost any required tone or shade. Almost all reptiles and amphibians possess the power of changing their hue in accordance with their environment in a very high degree; and among certain tree-toads and frogs it is difficult to say what is the normal colouring, as they vary indefinitely from buff and dove-colour to chocolate-brown, rose, and even lilac.
But of all the particoloured reptiles the chameleon is by far the best known, and on the whole the most remarkable for his inconstancy of coloration. Like a lacertine Vicar of Bray, he varies incontinently from buff to blue, and from blue back to orange again, under stress of circumstances. The mechanism of this curious change is extremely complex. Tiny corpuscles of different pigments are sometimes hidden in the depths of the chameleon's skin, and sometimes spread out on its surface in an interlacing network of brown or purple. In addition to this prime colouring matter, however, the animal also possesses a normal yellow pigment, and a bluish layer in the skin which acts like the iridium glass so largely employed by Dr. Salviati, being seen as straw-coloured with a transmitted light, but assuming a faint lilac tint against an opaque absorbent surface. While sleeping the chameleon becomes almost white in the shade, but if light falls upon him he slowly darkens by an automatic process. The movements of the corpuscles are governed by opposite nerves and muscles, which either cause them to bury themselves under the true skin, or to form an opaque ground behind the blue layer, or to spread out in a ramifying mass on the outer surface, and so produce as desired almost any necessary shade of grey, green, black, or yellow. It is an interesting fact that many chrysalids undergo precisely similar changes of colour in adaptation to the background against which they suspend themselves, being grey on a grey surface, green on a green one, and even half black and half red when hung up against pieces of particoloured paper.
Nothing could more beautifully prove the noble superiority of the human intellect than the fact that while our grouse are russet-brown to suit the bracken and heather, and our caterpillars green to suit the lettuce and the cabbage leaves, our British soldier should be wisely coated in brilliant scarlet to form an effective mark for the rifles of an enemy. Red is the easiest of all colours at which to aim from a great distance; and its selection by authority for the uniform of unfortunate Tommy Atkins reminds me of nothing so much as Mr. McClelland's exquisite suggestion that the peculiar brilliancy of the Indian river carps makes them serve 'as a better mark for kingfishers, terns, and other birds which are destined to keep the number of these fishes in check.' The idea of Providence and the Horse Guards conspiring to render any creature an easier target for the attacks of enemies is worthy of the decadent school of natural history, and cannot for a moment be dispassionately considered by a judicious critic. Nowadays we all know that the carp are decked in crimson and blue to please their partners, and that soldiers are dressed in brilliant red to please the æsthetic authorities who command them from a distance.
SEVEN-YEAR SLEEPERS
For many generations past that problematical animal, the toad-in-a-hole (literal, not culinary) has been one of the most familiar and interesting personages of contemporary folk-lore and popular natural history. From time to time he turns up afresh, with his own wonted perennial vigour, on paper at least, in company with the great sea-serpent, the big gooseberry, the shower of frogs, the two-headed calf, and all the other common objects of the country or the seaside in the silly season. No extraordinary natural phenomenon on earth was ever better vouched for—in the fashion rendered familiar to us by the Tichborne claimant—that is to say, no other could ever get a larger number of unprejudiced witnesses to swear positively and unreservedly in its favour. Unfortunately, however, swearing alone no longer settles causes offhand, as if by show of hands, 'the Ayes have it,' after the fashion prevalent in the good old days when the whole Hundred used to testify that of its certain knowledge John Nokes did not commit such and such a murder; whereupon John Nokes was forthwith acquitted accordingly. Nowadays, both justice and science have become more exacting; they insist upon the unpleasant and discourteous habit of cross-examining their witnesses (as if they doubted them, forsooth!), instead of accepting the witnesses' own simple assertion that it's all right, and there's no need for making a fuss about it. Did you yourself see the block of stone in which the toad is said to have been found, before the toad himself was actually extracted? Did you examine it all round to make quite sure there was no hole, or crack, or passage in it anywhere? Did you satisfy yourself after the toad was released from his close quarters that no such hole, or crack, or passage had been dexterously closed up, with intent to deceive, by plaster, cement, or other artificial composition? Did you ever offer the workmen who found it a nominal reward—say five shillings—for the first perfectly unanswerable specimen of a genuine unadulterated antediluvian toad? Have you got the toad now present, and can you produce him here in court (on writ of habeas corpus or otherwise), together with all the fragments of the stone or tree from which he was extracted? These are the disagreeable, prying, inquisitorial, I may even say insulting, questions with which a modern man of science is ready to assail the truthful and reputable gentlemen who venture to assert their discovery, in these degenerate days, of the ancient and unsophisticated toad-in-a-hole.
Now, the worst of it is that the gentlemen in question, being unfamiliar with what is technically described as scientific methods of investigation, are very apt to lose their temper when thus cross-questioned, and to reply, after the fashion