l 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 first appears a wholly
different and unexpected result."[27] 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
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.[28] Slender bodies, too, and the
lessened divergence of the furculum,[29] would slightly diminish the
spread of the wings, and so would affect the measurements taken. As the
wing-bones, moreover, are to some extent correlated with the beak and
the feet, the artificial selection of shortened beaks might tend to
shorten the wing as well as the feet. Under these circumstances how can
we be sure of the actual efficacy of use-inheritance? Surely selection
is as fully competent to effect slight changes in the direction of
use-inheritance as it undoubtedly is to effect great changes in direct
opposition to that alleged factor of evolution.

SHORTENED BREAST-BONE IN PIGEONS.

The shortening of the sternum in pigeons is attributed to disuse of the
flight muscles attached to it. The bone is only shortened by a third of
an inch, but this represents a very remarkable reduction in proportional
length, which Darwin estimates at from one-seventh to one-eighth, or
over 13 per cent. This marked reduction, too, quite unlike the slight
reduction of the wing-bones to which the other ends of the muscles are
attached, was universal in the eleven specimens measured by Darwin; and
the bone, though acknowledged to have been modified by artificial
selection in some breeds, is not so