hem.

The diminution of the duck's wing is not great even in the birds that
"never fly," and from this we must deduct the direct effect of disuse on
the individual during its lifetime. As Weismann suggests, the
_inherited_ portion of the change could only be ascertained by comparing
the bones, &c., of wild and tame ducks _similarly reared_. If individual
disuse diminished the weight of the duck's wing-bones by 9 per cent.
there would be nothing left to account for.

I suspect that investigation would reveal anomalies inconsistent with
the theory of use-inheritance. Thus according to Darwin's tables of
comparative weights and measurements[23] the leg-bones of the Penguin
duck have slightly diminished in length, although they have increased 39
per cent. in weight. Relatively to the weight of the skeleton, the
leg-bones have shortened in the tame breeds of ducks by over 5 per cent.
(and in two breeds by over 8 per cent.) although they have increased
more than 28 per cent. in proportional weight.[24] How can increased use
simultaneously shorten and thicken these bones? If the relative
shortening is attributed to a heavier skeleton, then the apparently
reduced weight of the wing-bones is fully accounted for by the same
circumstance, and disuse has had no inherited effect.

Another strange circumstance is that the wing-bones have diminished _in
length only_. The shortening is about 6 per cent. more than in the
shortened legs, and it amounts to 11 per cent. as compared with the
weight of the skeleton. Such a shortening should represent a reduction
of 29 per cent. in weight, whereas the actual reduction in the weight of
the wing-bones relatively to the weight of the skeleton is only 9 per
cent. even in the breeds that never fly. Independently of shortening,
the disused wing-bones have actually thickened or increased in weight.
In the Aylesbury duck the disproportion caused by these conflicting
changes is so great that the wing-bones are 47 per cent. heavier than
they should be if their weight had varied proportionally with their
length.[25] 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 un