length.1 The reduction in weight on which Darwin relies seems to be entirely due to the shortening, and this shortening appears to be irrelevant to disuse, since the wings of the Call duck are similarly shortened in their proportions by 12 per cent., although this bird habitually flies to such an extent that Darwin partly attributes the greatly increased weight of its wing-bones to increased use under domestication.

We find that all the changes are in the direction of shorter and thicker bones-a tendency which must be largely dependent upon the suspension of the rigorous elimination which keeps the

1 This excessive thickening under disuse appears to be due partly to a positive lateral enlargement or increase of proportional weight of about 7 per cent., and partly to a shortening of about 15 per cent. Carefully calculated, the reduction of the weight of the wingbones in this breed is only 8.3 per cent. relatively to the whole skeleton, or only 5 per cent. relatively to the skeleton minus legs and wings. The latter method is the more correct, since the excessive weight of the leg-bones increases the weight of the skeleton more than the diminished weight of the wing-bones reduces it.

bones of the wild duck long and light. The used leg-bones and the disused wing-bones have alike been shortened and thickened, though in different proportions. Natural or artificial selection might easily thicken legs without lengthening them, or shorten wings without eliminating strong heavy bones, but it can hardly be contended that use-inheritance has acted in such conflicting ways. The thickening of the wing-bones has actually more than kept pace with any increase of weight in the skeleton, in spite of the effect of individual disuse and of the alleged cumulative effect of ancestral disuse for hundreds of generations. The case of the duck deserves special attention as a crucial one, if only from the fact that in this instance, and in this instance only, has Darwin given the weights of the skeletons, thus furnishing the means for a closer examination of his details than is usually possible.

If we ignore such factors as selection, pan

mixia, correlation, and the effects of use and disuse during lifetime, and still regard the case of the domestic duck as a valid proof of the inheritance of the effects of use and disuse, we must also accept it as an equally valid proof that the effects of use and disuse are not inherited. Nay, we may even have to admit that, in two points out of four, the inherited effect of use and disuse on successive generations is exactly opposite to the immediate effect on the individual.

Among fowls the wing-bones have lost much in weight but little or nothing in length—which is the reverse of what has occurred in ducks, although disuse is alleged to be the common cause in both cases. Some of the fowls which fly least have their wing-bones as long as ever. In the case of the Silk and Frizzled fowls-ancient breeds which "cannot fly at all"-and in that of the Cochins, which "can hardly fly up to a low perch," Darwin observes "how truly the proportions of an organ

may be inherited although not fully exercised during many generations."1 In four out of twelve

breeds the wing-bones had become slightly heavier relatively to the leg-bones. Do not these facts tend to show that the changes in fowls' wings are due to fluctuating variability and selective influences rather than to a general law whereby the effects of disuse are cumulatively inherited?

PIGEONS' WINGS.

Concerning pigeons' wings Darwin says: “As fancy pigeons are generally confined in aviaries of moderate size, and as even when not confined they do not search for their own food, they must during many generations have used their wings incomparably less than the wild rock-pigeon. . . . but when we turn to the wings we find what at

1 Variation of Animals and Plants under Domestication, i. 284.

first appears a wholly different and unexpected result." This unexpected increase in the spread of the wings from tip to tip is due to the feathers, which have lengthened in spite of disuse. Excluding the feathers, the wings were shorter in seventeen instances, and longer in eight. But as artificial selection has lengthened the wings in some instances, why may it not it not have have shortened them in others? Wings with shortened bones would fold up more neatly than the long wings of the Carrier pigeon for instance, and so might unconsciously be favoured by fanciers. The selection of elegant birds with longer necks or bodies would cause a relative reduction in the wings as with the Pouter, where the wings have been greatly lengthened but not SO much as the body.2 Slender bodies, too, and the lessened divergence of the furculum,3 would

1 Variation of Animals and Plants under Domestication, i. 184, 185. 2 Ibid. i. 144, 145. 3 Ibid. i. 185.