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of the elaborate observations which have clusions. Without feeling it necessary validity of all the special explanations work, we must admit that the general the by a superabundance of inductive evidenc kind of selection is taken in connection protective concealment, we have the mea far the greater part of the colouring fo kingdom.

The colours of the vegetal kingdom hay extent, been no less satisfactorily expla not often need protection, but very often insects to fertilize them, and maintain powers in the greatest vigour. Their insects, as do also their sweet odours and and that this is the main function of shown by the striking fact that those pl perfectly fertilized by the wind, and do insects, rarely or never have gaily-coloured

Returning for one moment to the case are usually benefited by concealment b conspicuousness, let us note Prof. Shaler's tion of the rattlesnake's rattle. The appendage has long been a puzzle to philosop and Darwinians have been repeatedly challe for the formation or preservation by natural organ assumed to be injurious to the species. has lain in the assumption, too hastily made, of the rattle must be prejudicial to the st warning its enemies or prey of its present giving the enemies time for sudden attack, the prey to escape. On the theory of natural preservation of the species must entail the atro an organ, or, rather, must prevent its origination 1 Wallace, Natural Selection, p. 262.

insects by their disgusting taste, that they are exactly imitated by at least three genera of diurnal moths. In other parts of the world similar phenomena have been noticed. The relationship of the leptalis to the heliconia is repeated in India, in the Philippine Islands, in the Malay archipelago, and in various parts of Africa; the protected insect being, in all these cases, very much less numerous than the insect whose colours it mimics. In similar wise, bees and wasps are often imitated by beetles, by flies and even by moths.

For further details I must refer to Mr. Wallace's essay, which is a singularly beautiful specimen of inductive reasoning. The facts already cited are quite enough to sustain the general conclusion that the colours of animals are in the main determined by the exigencies of the struggle for existence. Where it is for the advantage of an animal to be concealed, as in the great majority of cases, its colour, whether brilliant or sombre, is such as to protect it. But where the animal is otherwise adequately protected-either by its peculiar habits, by a sting, a disgusting odour or taste, or a hard carapaceand where it is not needful for it to be hidden from the prey upon which it feeds, then there is usually no reference to protection in the colour of the animal. In some of these cases, however, a very conspicuous colouring becomes protective as in the case of the jet-black toad which Mr. Darwin saw in La Plata, which emitted a poisonous secretion, and which, when crawling over the sandy plain, could not fail to be recognized by every passing creature as an object to be avoided.

In many cases the gorgeous tints of the otherwise protected male animal are due to what is called "sexual selection,"to the continual selection of the more beautiful males by the females. To this cause is due the magnificent plumage of the male bird of paradise; and Mr. Darwin would similarly explain the brilliant colours of many male butterflies. In his work on the "Descent of Man" may be found an account

so that in a fierce struggle it will often happen that its action is not prompt enough to preclude a return of compliments fatal to the snake. When a tiger tears open the jugular vein of his enemy, the enemy is placed hors de combat at once; but when the rattlesnake has bitten, there is nothing to prevent the foe from employing his few remaining moments in tearing the serpent to pieces. Hence the rattlesnake must be peculiarly benefited by an apparatus which serves as a signal to warn enemies of his presence, and to keep them from attacking him. His more formidable enemies, belonging chiefly to the mammalian class, are certainly intelligent enough to profit by such warning and shun the danger; and as it is plainly for the snake's advantage to avoid even a conflict, it is clear that he is practically helped even less by his terrible bite than by his power of threatening a bite.

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This explanation seems to me quite sound in principle. Yet if we adopt it, there is nothing to prevent us from giving due` weight also to Prof. Shaler's suggestion. The success with which the note of the cicada is counterfeited by the rattle is a point to be more fully determined by further observation. And if it turns out that the rattle fulfils the double purpose of alarming sundry animals that are hostile and of enticing sundry others that are good for food, it will not be the first case in which it has happened that a structure useful in one way has also become useful in another way. The question is an interesting one, and valuable if only because it reminds us of the danger of reasoning too confidently, from à priori premises, about matters the due elucidation of which requires careful study of the details of the every-day life of animals. It is one of the great merits of the theory of natural selection that it has directed so many naturalists, with eyes open, into this fruitful field of inquiry.

It is because it so well illustrates the wealth of suggestiveness in Mr. Darwin's theory, that I have ventured upon this

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digression. To the general validity that theory to the validity of the more special pothesis concerning ::.uses of concealment or of conspicuousness, the success ! foregoing explanation is not essential-nce. '.. inadequacy may very well e due to the incommi-teness our grasp upon all the ietails of this partanter returning from this digression to our LAIK · sidering the general significance ie

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CHAPTER XI.

TWO OBJECTIONS CONSIDERED.

WHEN an objection to a complex theory in any d of science is so extremely obvious as to seem at fatal to the theory, it is unwise to urge it in argum we have very thoroughly considered the matter. Laplace and Goethe, Spencer and Darwin, in fram theories of evolution, are indeed liable to overlook di which are so unobtrusive as to be detected only a longed observation; but they are very unlikely to difficulties which are so conspicuous as to occur at the minds of a hundred general readers. When, there reader of average culture, who has perhaps never seri bent his mind to the question of the origin of species who is very likely unacquainted with the sciences w throw light upon that subject, finds himself immediat confronted by difficulties in a theory which men of t highest learning and capacity have spent a quarter of a cer tury in testing, common prudence should lead him to con tinue his study until he has made sure that the difficulty is not due to his own ignorance rather than to the shortcomings of the theory. This wholesome caution is too seldom manifested by literary reviewers, many of whom, in criticizing Mr. Darwin's theory without having duly read his works,

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