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of the worm was merely due to particles of the colouring substance of the host, which had passed out of the intestine of the worm into its skin.

We have thus a clue to a very simple theory of protective coloration, which may, at least, apply to lichen-like insects and to some leaf-feeders.

In any case, a necessary preliminary to all speculations about the meaning of colours is an investigation of the colours themselves. This seems to be a truism of so obvious a character as to be hardly worth mentioning; nevertheless one of the most neglected branches of zoology at present is the chemistry, and the laws which govern the distribution, of pigments. The theories of animal coloration have outstripped the fundamental facts by an enormous distance; indeed, it is almost forgotten that there are any such facts.

With regard to the special resemblance which is seen between tree-haunting animals and their surroundings, it is surprising to find how few instances there really are. This assertion may appear to be rather bold; but if we consider, firstly, the great prevalence of sandy-coloured animals in arid and sandy localities, and, secondly, the almost universal transparency of pelagic animals, the absence of a correspondingly large number of green animals among trees is not a little striking. In our Own country there are but few green .birds. Indeed there is not a single bright and uniformly green bird; but we cannot perhaps fairly make use of this instance, for Mr Wallace has pointed out that the deciduous foliage would expose green birds in the winter, and particularly in the early spring, when they are nesting and most need protection. But insects which only survive for a summer may be

reasonably taken as a crucial test. There is only one tree-frequenting butterfly which is green-viz., the Green Hair Streak and there the green colour is confined to the under surface of the wings; but this insect, like other butterflies when at rest, folds the wings together so as to expose only the lower surface: hence the protection is just as strong as if the entire insect were green. Among moths there is not, proportionately, a much greater number of greencoloured species. There are eight species of emerald moths, which are of a nearly uniform green colour, four or five Tortrices, with green upper wings (in a position of rest, the upper wings cover the lower), the two "Foresters," and a few Noctuæ, in which green forms a large component part of the coloration, in the upper wings at least. Green Lepidoptera do not appear to be relatively more abundant in tropical countries than they are with us. doubt, plenty of green beetles in all countries; but on turning over the plates which illustrate Mr Martin Jacoby's series of memoirs upon the phytophagous Coleoptera in the Proceedings of the Zoological Society,' one cannot help being struck by the marked absence of green among the members of this group. Mr Wallace quotes Dr Günther to the effect that tree-snakes, with the exception of the genus Dipsas, are entirely or largely green; but the tree-frogs comprise a large number of forms that are most conspicuous; and even among those that are green, striking marks of another colour must largely do away with the protective value of the green colour. There is, at the time of writing, a large Australian treefrog in the Reptile House at the Zoological Gardens, in which the utility of the green colour must be

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largely interfered with by a series of white marks and patches along the side. These marks might suggest a fungus growing upon a green leaf to an enemy of a turn of mind too inquiring for the safety of the frog; but perhaps the enemy would be aware that it was somewhat unusual to find mildew upon a green leaf. As to birds, it is quite true that there are green arboreal species in tropical countries; but the most that can be said about the matter is, that there are a good many birds so coloured. Arrived at this point, the reader will probably assume that these few facts have been brought together for the purpose of trying to throw discredit upon the theory that a green coloration has been gradually acquired for protective purposes. An advocate of this theory will at once triumphantly point out a large number of omissions from the above very scanty list. It seems to me, however, that a prevalence of green among arboreal animals cannot be proved; and thus there might appear to be a certain weakness in the theory of protective coloration as applied to these instances. Paradoxical though it may sound, I am of opinion that the apparent weakness of the arguments constitute the real strength of the theory. It is precisely because the isabelline colour of desert animals and the transparency of pelagic organisms is so universal that some general environmental cause appears to be necessary for the explanation of the facts. On the other hand, the picking and choosing among arboreal animals is distinctly suggestive of natural selection. There are quite enough instances of a green colour among tree-living creatures to call for some theory to explain the facts, but there are not too many to render selection improbable.

There are, however, two important questions that must be answered before we can fairly put down to the action of natural selection the occasional green colour of tree animals.

Firstly, Are there any grounds for referring the coloration to the direct effects of food, or to any other similar cause which might equally affect all the inhabitants of trees? As explained already, our knowledge of the pigments of animals does not at present allow of a definite answer to this question. This much, however, is certain: that the green colour of the iguana and of several other forms is not the same substance as the "chlorophyll" of leaves. Indeed, the pigment in the skin of the iguana is really yellow, or at least some of the pigment is; so the green effect is produced by a combination of colours.

The second question is really of equal importance: Is the green colour useful? If it be proved to be superfluous, there is obviously an end of all theories based upon utility. Natural selection could not be accused of forming and perpetuating a plan of coloration that was useless to its possessor.

There is a decided tendency to assume that, if a colour resemblance exist, it must be useful. A contributor to 'Nature' pointed out some years since a singular resemblance between a particular caterpillar found in India and a shrew. The assumption was that the caterpillar was protected from these very animals by its likeness to them. The protection would have to be proved first. But in the meantime, shrews have a keen smell, as far as we can judge by the structure of their brain, and by the fact that they are highly odoriferous; and even if they were taken in by the appearance of the

much in the long-run, for shrews are a pugnacious race.

caterpillar, it would not score ingly" coloured, and need not and do not show any particular wariness; and in most parts of the world tree-frogs could get on very comfortably if they were limited to a diet of wasp. As to the protection from snakes, it is not stated in the above-quoted passage, nor in the context, how far the snakes in question will take their prey when at rest. Snakes generally make their fatal spring upon a moving animal only. In this case, no amount of protective colour would be of the very least use.

We must therefore inquire into each case separately, and not hastily assume a law of general application. The green of the treefrogs may be useful for both aggressive and protective purposes. Mr Poulton, in his very interesting work upon the colours of animals, suggests that "the green tree-frog is probably aided in capturing the insects on which it feeds because of its close resemblance to the leaves around it; but it is also protected in the same manner from the animals which prey upon it. Thus Mr E. A. Minchin tells me, from his experience in India, that tree-frogs are sought for with especial eagerness by snakes, which greatly prefer them to others."

It is a matter of the greatest difficulty to decide upon the nature of the vision of insects. This is indeed another branch of zoology which ought to be followed out before any theories, which are based upon what is entirely an anthropomorphic conception of insect vision, are even thought of, much less preached as gospel. Common experience is that insects will buzz round the most dangerous enemy of their race so long as he remains quiet. A slight movement will drive them away helter-skelter. Here common observation accords with the detailed investigations of M. Plateau, who will hardly allow even the highest of insects more than a general notion of light and shadows, and a perception of the direction of movement of bodies. Besides, it has been lately stated in Na ture' that tree-frogs show an especial greediness for wasps, with which they will gorge themselves to repletion. Wasps are

warn

On a priori grounds the protective advantage of a green colour to the iguana would seem to be obvious. Resting as it does habitually in a motionless attitude upon the branch of a tree, the colour would render it invisible. In the island of St Lucia, in the West Indies, there is a species of iguana which is highly prized as an article of food; the white flesh of this reptile has been compared for delicacy of flavour with that of a young chicken. The lizard is hunted by means of dogs which are quite unable to see their prey: they detect its whereabouts, however, by the sense of smell; and, indeed, many reptiles have a strong odour. Now in South America there are also green and brown iguanas: a brown colour is quite as advantageous for protective purposes as a green colour in this case, perhaps even more So. They are probably sought after by jaguars and other arboreal cats. The cat tribe, it is true, do not hunt so entirely by scent as dogs do; but the structure of their brain shows an almost equally well-developed condition of that part of the brain which is concerned with the sense of smell. In fact, all these mammals have been distinguished as "osmatic

from such creatures as ourselves and the monkeys, in which the "rhinencephalon" is small. It seems, therefore, probable that here too the protective coloration is not so useful as it might at first appear to be.

At any rate, the utility of each instance has to be clearly proved; though, as already suggested, there are considerable probabilities in favour of the action of natural selection in causing, or at least in intensifying, such protective resemblances as are shown by many green arboreal animals.

But does the theory hold good in the case of pelagic organisms? Here we have an apparent adaptation to circumstances that is much more widely spread—indeed, nearly universal. This very fact is against the interpretation that has been advanced by Mr Wallace and others. We should naturally expect to find here as elsewhere various means of defence. The struggle for existence is just as relentless on the smooth surfacewaters of mid- ocean as in the heart of a tropical forest: competition there is just as keen. And yet, with a singular unanimity nearly all the surface organisms have, so to speak, selected one means of protection-and one only. Tried by the test of utility, there would seem to be no special advantage in transparency to the pelagic creatures. Their enemies are principally themselves; they prey upon one another, and the survivors are apt to be engulfed wholesale by a whale, or porpoise, or by a school of mackerel or herring. Now, a whale does not stop to consider what it shall take and what it shall leave; it simply opens its mouth as it rushes through the water, and takes what it can get, which is plenty. Neither do the herrings or mackerel; their stomachs

contain an abundance of the minute organisms of the sea, which they swallow without regard to species or genera, and without regard to comparative invisibility or visibility. An absolutely perfect transparency would not avail the pelagic organism against a shoal of predaceous fish. As to their internecine combats, we must always bear in mind relativity of size. To us the surface waters appear on a casual inspection to be devoid of life; but a minute shrimp would be able to see through a transparent pelagic worm in more senses than one. Besides, if transparency were so advantageous in the surface-waters, it would be at least as advantageous at the bottom; and yet we do not find a marked prevalence of transparent animals adherent to or crawling over the rocks and sand which form the bed of the ocean.

We must therefore, for the present, exclude the transparency of pelagic animals from those effects which may be provisionally put down to natural selection.

And I am disposed to think that the sandy hue of desert animals must go the same way.

There are some facts which tend to prove that a damp atmosphere darkens colour, and that a dry atmosphere bleaches it. Melanic varieties, as they are termed, often occur on islands and other situations where the climate is moist as well as warm. There is an excellent instance of this in the Zoological Gardens at present: it is a lizard from one of the islands of the Canary group, which is closely allied to the eyed lizard of Southern Europe. The black coloration of Simony's lizard is paralleled in the case of some varieties which are found in the islands of the Mediterranean.

FRANK E. BEDDARD.

PORTUGUESE REPUBLICANISM AND THE MILITARY REVOLT.

UNTIL a couple of years ago a Republic in Portugal was a possibility which amongst the general public was rarely even mentioned; and if now and then such a thing became the subject of conversation, it appeared to have but little interest even for those theoretically inclined to that form of government. Under this calm exterior there were doubtless many men planning and working for ends which had apparently little prospect of realisation; but the masses were too ignorant and backward to take fire at the idea, and seemed content to go on for an indefinite future as they had done in the past, distrusting and abusing with the utmost impartiality whichever party happened to be in power. It was only when their endurance was more than usually tried by some new tax or the neglect of some absolutely necessary public work, that they sighed for the Utopia which, according to their confused ideas, a republic would at once create. "What is a republic?" a workman was overheard to ask a comrade. "A republic," was the reply, "is where each one does as he likes and no one pays taxes." This may be taken as a fairly accurate definition of the opinions held by the lower classes on the subject. They of course knew absolutely nothing of history or political economy, and would have been incapable of understanding the most simple explanations of these subjects; thus a republic appeared to them as a far-off Paradise, but a Paradise which they had to people and furnish according to their own

I.

ideas of what constitutes happiness. A step higher came the reading and writing class, the small shopkeepers and their assistants: these were largely in favour of a change, as were also the artisans and factory-hands; but the time had not yet arrived for them to publicly express their opinions, and little was heard of them. fairs might have continued in this state for a long time, but for unexpected events which swept the land like a moral hurricane, and made their effects felt in every grade of society.

Af

The first of these was the proclamation of the Brazilian Republic. The mutterings of the coming storm had been but indistinctly heard and attracted little attention, so that the sudden announcement of the revolution and its perfect success produced far more sensation than if it had been generally expected. Brazil and Portugal are so closely connected that the influence of this sudden change, though not showing on the surface, must on no account be underrated. It was of course a great encouragement to the Portuguese republicans; and more important still, it showed the nation that a complete change of government might be effected almost without bloodshed, and with comparatively little danger or interruption to trade. Many persons who would put up with what they consider the continued failure of monarchical government rather than risk the terrible calamity of a civil war, would have no scruples in helping to overturn a tottering throne if convinced that it could

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