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.