Before leaving the subject of the dark vein scales, it may be desirable again to refer to the folding of the wings in the pupa state; for although the pattern is not supposed to be the result of the plications, yet the compressed condition of every part of the wing, whilst in the chrysalis, must be borne in mind. The divergence of a portion of the vein scales to form scallops is difficult to be conceived if we regard the process as wrought in the fully expanded wing; but the whole scallop is a microscopic speck, and the direction of the divergence quite indistinguishable in the pupa state. Yet in this state, whilst the vessels are soft and permeable, the scheme of the future pattern is, no doubt, fully organized, so that the most minute extension this way or that from the incipient vein, of the dark pigment bearing germs of scales, when inflated, expanded, dried and hardened in the wing of the imago, becomes a band, or a scallop, or a ring, according to the original construction and direction.

From the vein scales, then, are supposed to arise all the darker markings which limit and sometimes enclose the areas occupied by the paler ground-tint; frequently, in fact, extending over the greater portion of the surface of the wing. These darker markings are manifestly affected by the passage of the veins, and very commonly, though not always, are distinguished by an outline more or less sharp and distinct.

We come now to inquire into the modifications observable in the paler ground-colour, proper to the scales growing on the spaces between the veins, and often extending over the veins themselves. The first and most obvious modification is the deepening or intensifying of the colour in certain parts of the wing: thus, yellow becomes bright orange; white becomes yellow or scarlet; a pale buff becomes bright testaceous, &c. The transition is generally gradual, the richer being shaded off at its edges into the paler colour. Indeed, so characteristic of the ground-pattern is this kind of shading, that I propose to call the area occupied by the brighter and more intense hue, the "blush." A very satisfactory example of the blush is seen in Gonepteryx Cleopatra.

Belonging essentially to the membranous portions of the wing, the blush should not in its contour be affected by the veins, and for the most part it seems to be remarkably independent of them. It occurs in all parts of the wing, at the tip or in the disc, at the margin or, less frequently, near the base, often at the anal angle of the hind wing; but wherever it occurs, it seems to be neither limited nor extended by the veins. It is of course liable, like the ground-colour to which it belongs, to be parted into bands or spots by the dark vein scales; in fact, the whole area of the blush is seldom seen, and more frequently than otherwise the junction of the blush with the pale tint, or rather the space where the junction

might have been, is occupied by expanded parts of the black venous pattern.

The blush is not always shaded at its junction with the paler tint, especially where it takes the form of a patch or a spot; as in the tip of the fore-wing of the male of Anthocharis Cardamines, the spot in the fore-wing of Gonepteryx Rhamni, and that on the anal angle of the hind-wing of Papilio Machaon.

In Vanessa Cardui the blush is suffused over the greater part of the fore and hind wings, the pale ground colour appearing in spots towards the tip of the fore-wing, on the under side of which the "blush" character of the rose-tint is more plainly exhibited.

In Vanessa Atalanta a similar disposition of colours is observable, but the black vein-scales cover a larger portion of the wings, the bright scarlet of the blush being shown in a band on the fore-wing and on the margin of the hind-wing.

*

The shading of the paler into the brighter hue is well seen in Vanessa Urticæ.

The testaceous colour of the Fritillaries I am inclined to regard as a blush, uniformly suffused over the whole area of the wings. The dependence of the black scales on the veins is seen throughout the tribe.

In Papilio Hector the blush is exhibited in the crimson spots on the hind wings.

In Thais Rumina the blush is broken up into spots, but it will be observed that the crimson spots have black edges, and are rarely bordered by the yellow ground-colour.

We have now observed three important elements in the colour patterns of butterflies: the pale ground-colour; the dark markings due to the vein scales; and the more or less richly-tinted blush; a fourth remains to be noticed.

Hitherto, the scales themselves have presented no very marked distinctions; the black scales, colour excepted, are in appearance exactly similar to the adjacent white or red ones. Under a magnifying power and by transmitted light, all are found to contain appropriate colouring matter; thus, an orange band is made up of orange-coloured scales, and a black marking of dark and nearly opaque scales.

But conspicuous on the wings of butterflies are certain other hues, and these the most splendid of any, which when examined by transmitted light are found to be produced by scales not of corresponding colours. Lycæna Adonis, the most brilliant of the British "Blues," has scales altogether colourless; the deep purple on the wings of Apatura Iris is produced by scales the colouring matter of

That the scarlet band is a blush, shown as it were through an opening in the black scales, appears from the under-side of the fore-wing. This is seen still more plainly in the allied species Pyrameis Gonerilla from New Zealand. 2 A

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which is brownish black. A similar hue on Thecla Quercus is formed by scales the colour of a dark cloud. The brightest scales on Lycana Phleas are of a watery burnt-sienna hue. Far more striking discrepancies between the transmitted and reflected hues of scales might be quoted from exotic butterflies: I have selected these because the insects are more familiarly known. Viewed as opaque objects, even under a moderately high magnifying power, at the proper angle the reflected hue comes out superbly, but when the light is sent through the scales, a pale, or dull dark tint is all that is observable.

These scales therefore exhibit the phenomena of iridescence, and their hues are derived, not from the colouring matter present in them, but from striations upon their surfaces; not, however, from the stria which under a microscope may be seen on all Lepidopterous scales, but from others far more minute, surpassing, probably, in delicacy and uniformity, anything elsewhere to be found in nature. The surfaces of iridescent bodies, such as mother-of-pearl and some of the ores of iron and copper are often very gorgeously tinted, but their hues are mixed and irregular, whereas nothing can exceed the purity of colour exhibited by patches of these iridescent scales, indicating a wondrous exactness in the intervals between the striæ.

For convenience, I shall call the feature produced in the colourpattern by these iridescent scales, the "gloss."

The gloss seems to have towards the dark vein scales the same kind of relation which the blush has towards the pale ground-colour, except that it seems to be rather charged upon, than shaded off into, the venous scales, being sometimes, as it were, sprinkled or dusted upon them, as in Papilio Paris and Teinopalpus imperialis.

The gloss is rarely seen to form sharply-defined bands or patches, nor does it often come in contact with the ground-colour or the blush, being almost always surrounded by a black border: it frequently suffuses the whole wing,* and is often pierced by the black vein scales, which show themselves as spots in the midst of it.

In rare instances, highly-coloured scales, belonging to the blush, exhibit iridescence; when this occurs the result is exquisitely beautiful. Thus, in Papilio Vertumnus, a patch of carmine scales on the hind-wing is glossed so as to show an amethystine hue when seen obliquely; and in one rare species of Ornithoptera the yellow patch on the hind-wing has similar reflections. In these butterflies the carmine and yellow hues are the results of corresponding pigment granules; the amethystine gloss arising from iridescent striæ on the surfaces of the scales which contain the pigment grains.

It is a source of much gratification in all branches of natural history, to observe the modifications of an organ through a series of

*As in some Morphos and many of the Lycanidæ.

species, in one or other of which it may become so changed in appearance, that its identification is possible only by a close comparison between the many links which connect its most abnormal forms with those in which it is ordinarily found.

I have often felt the want of a rationale of this kind, in admiring the colour-patterns of butterflies, and have endeavoured to trace a kind of homology between their respective constituents.

For a long time the case seemed hopeless; but opportunities having been afforded me of examining a moderately large number of Rhopalocera from most parts of the world where they abound, many apparent anomalies were found to be so only because intermediate forms had not previously been known to me. Thus, for instance, I have ventured to speak of the red spot at the anal angle of the hind-wing of our British Swallow-tailed Butterfly as a form of the "blush." British butterflies alone considered, this must appear to be simply fanciful; but any one who will examine even a limited number of species of the large genus Papilio will, I think, be satisfied that the red spot on the hind wing of P. Machaon is a modification of the richer tinting of the pale ground-colour, such as may be seen in its more ordinary form in P. Zagreus (Doubleday), and in a striking intermediate form in P. Iswara (White).

I have only touched on the elementary portion of the subject; more minute details must be reserved for another occasion; but I venture to hope that the present very imperfect account of an attempt to classify the colour-patterns of butterflies may not be uninteresting to their admirers, and may lead to further investigations by more able observers.

IV. THE MODERN ASPECTS OF PHYSICAL SCIENCE. If we examine with thoughtful deliberation the aspects of Physical Science as they are now presented to our mental vision, we arrive at the conclusion that much uncertainty surrounds them, and we feel that with the advance of knowledge we shall have to modify many a pet hypothesis and, possibly, to abandon some favourite theories which have held their position by the weight of the great names by which they have been supported.

We have before us ten works, each one of them excellent in its class,* and in their entirety fairly representing the conditions of the

* 1. 'The Elements of Natural Philosophy; or, an Introduction to the Study of the Physical Sciences.' By Charles Brooke, M.A., M.B., F.R.S. Churchill. 2. Heat considered as a Mode of Motion.' By John Tyndall, F.R.S. Longmans.

3. 'Faraday as a Discoverer.' By John Tyndall. Longmans.

Physical Science of the present day; and it is from a careful study of those, that we arrive at the conclusion that the present is a transition period. We have included in our list some recent works on Chemistry. When the reader reflects on the phenomena connected with the socalled molecular forces-embracing especially those of capillary attraction, of exosmose and endosmose, of epipolic action or surface force, of all that belongs to the allotropic state, and of the facts connected with diffusion and transpiration-he will feel that Physics claims a large portion of the domain of Chemistry as its own. The influences of Light, Heat, and Electricity, in producing chemical changes, and again the development of those energies by chemical action, prove the close alliance of Physical and Chemical Science in all that relates to the properties of molecules and masses. It is on this account-although we may not, in this article, make any further reference to them-that we have included Watts's admirable 'Dictionary of Chemistry' and Dr. Hofmann's excellent little volume, as the exponents of the principles-it might be better to write the philosophy-of this science. Our desire is to stimulate inquiry, to invite search, and to show that amongst the authorities in science there exist great differences of opinion upon some most important questions. Therefore we have selected those works which most fully and satisfactorily set forth the philosophy of modern Physical Science as the basis of our remarks.

It is universally admitted that we live in a transition period. Old things are being roughly examined, and in many cases subverted, while the New is only, as yet, upon trial. As the political atmosphere exhibits unmistakable tendencies towards a storm, all the elements of which are surely gathering upon the horizon, so the philosophical atmosphere is disturbed by the conflict of opposing currents of thought, which threaten a cyclonic movement likely to carry destruction as it passes, through many a favoured field. Some of our social organizations, stamped with the approval of centuries, and which have hitherto been, through the sanctifying powers of age, regarded with feelings of superstitious reverence, are being rudely shaken. It is clear that many of them will perish in the storm; but it is not so clear that those systems which will occupy the ground they filled are destined to endure so long, or to serve

4. The Reign of Law.' By the Duke of Argyll. Strachan.

5. A Treatise on Frictional Electricity.' By the late Sir Wm. Snow Harris ; edited by Charles Tomlinson, F.R.S. Virtue.

6. Researches on Solar Physics.' By Warren De la Rue, F.R.S.; Balfour Stewart, F.R.S.; and Benjamin Loewy. Printed for private circulation.

7. A Dictionary of Chemistry.' By Henry Watts, F.R.S., &c. Longmans. 8. Introduction to Modern Chemistry, &c.' By A. W. Hofmann, LL.D., F.R.S. Walton & Maberley.

9. Reports of the British Association.'

10. Philosophical Transactions of the Royal Society.'