There are no parts of Mr. Darwin's ingenious book in which he gives the reins more completely to his fancy than where he deals with the improvement of instinct by his principle of natural selection. We need but instance his assumption, without a fact on which to build it, that the marvellous skill of the honey-bee in constructing its cells is thus obtained, and the slave-making habits of the Formica Polyerges thus formed. There seems to be no limit here to the exuberance of his fancy, and we cannot but think that we detect one of those hints by which Mr. Darwin indicates the application of his system from the lower animals to man himself, when he dwells so pointedly upon the fact that it is always the _black_ ant which is enslaved by his other coloured and more fortunate brethren. "The slaves are black!" We believe that, if we had Mr. Darwin in the witness-box, and could subject him to a moderate cross-examination, we should find that he believed that the tendency of the lighter-coloured races of mankind to prosecute the negro slave-trade was really a remains, in their more favoured condition, of the "extraordinary and odious instinct" which had possessed them before they had been "improved by natural selection" from Formica Polyerges into Homo. This at least is very much the way in which (p. 479) he slips in quite incidentally the true identity of man with the horse, the bat, and the porpoise:-- The framework of bones being the same in the hand of a man, wing of a bat, fin of a porpoise, and leg of the horse, the same number of vertebrae forming the neck of the giraffe and of the elephant, and innumerable other such facts, at once explain themselves on the theory of descent with slow and slight successive modifications.--p. 479. Such assumptions as these, we once more repeat, are most dishonourable and injurious to science; and though, out of respect to Mr. Darwin's high character and to the tone of his work, we have felt it right to weigh the "argument" again set by him before us in the simple scales of logical examination, yet we must remind him that the view is not a new one, and that it has already been treated with admirable humour when propounded by another of his name and of his lineage. We do not think that, with all his matchless ingenuity, Mr. Darwin has found any instance which so well illustrates his own theory of the improved descendant under the elevating influences of natural selection exterminating the progenitor whose specialities he has exaggerated as he himself affords us in this work. For if we go back two generations we find the ingenious grandsire of the author of the _Origin of Species_ speculating on the same subject, and almost in the same manner with his more daring descendant. * * * * *