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but which we could never hope to understand. We now know that they benefit their possessor, and that they are perfected by Natural Selection, though the external "conditions" which give origin to the variations are not yet understood. Mr T. W. Wood states that the chrysalides of butterflies possess a most astonishing means of eluding observation, their shells being photographically sensitive for a short time after the caterpillars' skins have been shed, so that each individual assumes the colour most prevalent in its immediate vicinity. At a meeting of the Entomological Society he exhibited a great number of chrysalides of the two common species of white butterflies, taken from the stone-coloured sides of a house: against one of the sides a grape-vine was trained, and here the chrysalides of both species were green, being affected by the light shining through the leaves, while on the bare side of the house not a single green specimen could be found; and a glance at them conveyed an accurate idea of the colour of the surface to which they were attached. Mr Wood has noticed that the chrysalis of the small tortoise shell (Vanessa urtica), is golden only when found amongst nettles; for when on walls, palings, tree-banks, &c., it invariably partakes of their colours and general appearance of surface. The same remark may be made of the large tortoise shell (Vanessa polychloris), which, when found amongst leaves, is of the colour of a withered elm leaf, with a few silver spots, though when found on walls, &c., the whole colouring is different and the spots are absent. Some experiments made by rearing caterpillars and placing them in coloured boxes exposed to sunlight, showed results in accordance with these facts.1

1 The Student, September 1868.

CHEMISTRY OF ASSIMILATIVE COLOURING.

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It seems probable, then, that the chemistry of nature, going beyond the results attained by man, accomplishes photography in colours; and although this does not explain imitative forms, it reminds us that all effects admit in their nature of being explained.

With a right view of creation, we find no difficulty in this; satisfied that the lines of causation centre in the chambers of the Eternal, we do not expect to shorten the distance by cutting the lines; and possessing no evidence of the existence of other human minds excepting in results which have their physical causes, we do not consider Divine Intelligence excluded because we find out how "mimicry" is accomplished. We admire the wondrous chemistry which accomplishes such magical effects, and in the protection afforded we see something to set against the existence of enemies. Observe the principle on which this assimilative colouring is distributed. It seems not to be given to animals whose habits do not expose them to special danger, nor to any which are endowed with other more effective means of escape. This is what the Duke of Argyll calls "the higher law of purpose which governs the lesser law, whatever it may be, by which assimilative colouring is produced." Birds whose habitat is the open plain or treeless moor, where the hawk has uninterrupted range for his sight and free scope for his great powers of wing, and who cannot retreat to any covert when taken at a disadvantage-these are almost the only birds which have their plumage assimilated to the general tinting and mottling of the ground on which they lie and feed. Observe, again, the apparent ease with which protection is given. In the leaf-like mantis there is no departure from the type of insects of the same order; but the

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whole effect is produced by a little elongation here, a little swelling there, a little dwarfing of one part, a little development of another. The most striking part of the whole imitation-that of the "nervation" of the leafis produced by a modification, not very violent, of a structure which belongs to all flying insects! It may occur to some minds that many other insects, birds, &c., might be benefited by the same kind of resemblance to inanimate objects, or mimicry of creatures not liable to attack; but there is a reason against this. The imitators must be few, or they will soon be found out; the measure of their increase is the measure of their danger. If the imitating butterflies, for instance, were to the imitated as two to one, the birds would soon find out that two butterflies in three were eatable, and although the third was nauseous, they would venture when they were hungry.

Growth of Instincts.-The savage instinct of the queen bee urges her to destroy the young queens, her daughters, as soon as born, or to perish herself in the combat. The instinct of the worker bees leads them to slaughter all the drones, their brothers, after the queen is fertilized. Maternal and sisterly hatred are not admirable, but fortunately they are rare, and even in the instances cited they serve so good a purpose that Mr Darwin is probably right in saying we ought to admire their action -it is undoubtedly for the good of the community that useless drones and supernumerary queens should die, and love or hatred is all the same to the inexorable principle of Natural Selection.1 Very well. Then can it be without beneficent arrangement that in the generality of cases love and not hatred works for the good of 1 Origin of Species, chapter vi.

INSTINCT A DOUBLE BLESSING.

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the community, almost every animal loving its young, and the little ones delighting to play together? The most unsocial brute will protect its own offspring, and happiness is never better exhibited than by young animals, such as puppies, kittens, and lambs, when playing together like our own children.

Instinct is, first of all, for the good of the individual possessing it is to it a possession of accumulated wealth stored by many generations of ancestors, and which, in place of becoming squandered, is increased by daily use and handed down to generations following. When social instincts arise, the community is enriched without the individual being robbed, for the wealth of all is enjoyed by each in his measure (receiving back from the common fund), besides which there is a present pleasure to the individual in the very exercise of instinct which is enriching the tribe. Were it not for the springing up of social instincts man himself would never have become civilized, moral and religious, but each individual would have been a brute, and worse than an isolated Ishmaelite amongst brutes.

If we looked at every instinct separately, we should find it to be for the good of its possessor, or of the species to which he belongs. The instinct which leads the hive bee to make hexagonal cells is an instinct which leads to the greatest economy of wax; so that, in times of plenty, the community is saved unnecessary trouble, and in times of scarcity is preserved, where others would not survive. The nest-building instinct among birds, the nut-burying instinct of squirrels, the hare-hunting instinct of a dog, are all for the advantage of both the individual and the species; and even the acquired instincts of domestic animals, such as that of

the shepherd dog, which leads it to drive and run round a flock instead of worrying them, is for the good of the dog in being for the good of his master, and evidently gives delight to the animal itself. It is not necessary to fill a chapter with instances, since these are sufficiently well known to all readers, but only to point out how Evolution makes the beneficence of instinct the more conspicuous by showing that instead of being bestowed by instantaneous fiat, it could only be given through long persistent working and great patience.

Variety in Nature.—Compare all the millions of faces of men and women, and no two will be found alike'; but if it follows from this that a perfect beauty must be a prodigy, we are not without some compensation. The great anatomist Bichat long ago said that if every one were cast in the same mould there would be no such thing as beauty. If all our women were to become as beautiful as the Venus de Medici, we should for a time be charmed; but we should soon wish for variety; and as soon as we had obtained variety we should wish to see certain characters that pleased us a little exaggerated beyond the then existing common standard.

It would appear that birds and all creatures who possess sufficient mental power to discriminate are as fond of variety as ourselves, for it is to sexual selection that Mr Darwin traces the marvellous variety in the colours and ornaments of the males. It would even appear, he says, that mere novelty, or change for the sake of change, has sometimes acted like a charm on female birds, in the same manner as changes of fashion with us.1 "Among the humming-birds different parts of the plumage have been selected in different genera as the 1 Descent of Man, ii. 230.

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