to maintain the uniformity of type in the case of the fore-limb as
previously explained, and should we not expect that in other and similar
cases a similar method should have been followed? Yet we repeatedly find
that this is not the case. Even in the whale, as we have seen, the
hind-limbs are either altogether absent or dwindled almost to nothing;
and it is impossible to see in what respect the hind-limbs are of any
less ideal value than the fore-limbs--which are carefully preserved in
all vertebrated animals except the snakes, and the extinct _Dinornis_,
where again we meet in this particular with a sudden and sublime
indifference to the maintenance of a typical structure. (Fig. 6.)[4] Now
I say that if the theory of ideal types is true, we have in these facts
evidence of a most unreasonable inconsistency. But the theory of descent
with continued adaptive modification fully explains all the known cases;
for in every case the degree of divergence from the typical structure
which an organism presents corresponds, in a general way, with the
length of time during which the divergence has been going on. Thus we
scarcely ever meet with any great departure from the typical form with
respect to one of the organs, without some of the other organs being so
far modified as of themselves to indicate, on the supposition of
descent with modification, that the animal or plant must have been
subject to the modifying influences for an enormously long series of
generations. And this combined testimony of a number of organs in the
same organism is what the theory of descent would lead us to expect,
while the rival theory of design can offer no explanation of the fact,
that when one organ shows a conspicuous departure from the supposed
ideal type, some of the other organs in the same organism should tend to
keep it company by doing likewise.

[4] It is, however, probable that all species of the genus retained
a tiny rudiment of wings in greatly dwindled scapulo-coracoid bones.
And Mr. H. O. Forbes has detected, in a recently exhumed specimen of
the latter, an indication of the glenoid cavity, for the
articulation of an extremely aborted humerus. (See _Nature_, Jan.
14th, 1892.)

[Illustration: FIG. 6.--Skeleton of _Dinornis gravis_, 1/16 nat.
size. Drawn from nature (_Brit. Mus._). As separate cuts on a larger
scale are shown, 1st, the sternum, as this appears in mounted
skeletons, and, 2nd, the