r, are represented? how much more reasonable is the naturalistic
interpretation; for here the very irregularity of their appearance in
different species, which constitutes rudimentary structures one of the
crowning difficulties to the theory of special design, furnishes the
best possible evidence in favour of hereditary descent; seeing that this
irregularity then becomes what may be termed the anticipated expression
of progressive dwindling due to inutility. Thus, for example, to return
to the case of wings, we have already seen that in an extinct genus of
bird, _dinornis_, these organs were reduced to such an extent as to
leave it still doubtful whether so much as the tiny rudiment
hypothetically supplied to fig. 6 (p. 61) was present in all the
species. And here is another well-known case of another genus of still
existing bird, which, as was the case with _dinornis_, occurs only in
new zealand. (Fig. 9.) Upon this island there are no four-footed
enemies--either existing or extinct--to escape from which the wings of
birds would be of any service. Consequently we can understand why on
this island we should meet with such a remarkable dwindling away of
wings.

[Illustration: FIG. 9.--_Apteryx Australis._ Drawn from life in the
Zoological Gardens, 1/8 nat. size. The external wing is drawn to a
scale in the upper part of the cut. The surroundings are supplied
from the most recent descriptions.]

Similarly, the logger-headed duck of South America can only flap along
the surface of the water, having its wings considerably reduced though
less so than the _Apteryx_ of New Zealand. But here the interesting fact
is that the young birds are able to fly perfectly well. Now, in
accordance with a general law to be considered in a future chapter, the
life-history of an individual organism is a kind of condensed
recapitulation of the life-history of its species. Consequently, we can
understand why the little chickens of the logger-headed duck are able to
fly like all other ducks, while their parents are only able to flap
along the surface of the water.

Facts analogous to this reduction of wings in birds which have no
further use for them, are to be met with also in insects under similar
circumstances. Thus, there are on the island of Madeira somewhere
between 500 and 600 species of beetles, which are in large part
peculiar to that island, though related to other--and therefore
presumably parent--species on the nei