sonorous vibrations of the
atmosphere, and indeed they are reduced, or have degenerated, to a
degree which makes it difficult to conceive how such vibrations can be
propagated to the ear-drum during the brief moments in which the opening
may be raised above the water."

[Illustration: FIG. 8.--Rudimentary or vestigial hind-limbs of
Python, as exhibited in the skeleton and on the external surface of
the animal. Drawn from nature, 1/4 nat. size (_Zoological
Gardens_).]

Now, rudimentary organs of this kind are of such frequent occurrence,
that almost every species presents one or more of them--usually, indeed,
a considerable number. How, then, are they to be accounted for? of
course the theory of descent with adaptive modification has a simple
answer to supply--namely, that when, from changed conditions of life, an
organ which was previously useful becomes useless, it will be suffered
to dwindle away in successive generations, under the influence of
certain natural causes which we shall have to consider in future
chapters. On the other hand, the theory of special creation can only
maintain that these rudiments are formed for the sake of adhering to an
ideal type. Now, here again the former theory appears to be triumphant
over the latter; for, without waiting to dispute the wisdom of making
dwarfed and useless structures merely for the whimsical motive assigned,
surely if such a method were adopted in so many cases, we should expect
that in consistency it would be adopted in all cases. This reasonable
expectation, however, is far from being realized. We have already seen
that in numberless cases, such as that of the fore-limbs of serpents, no
vestige of a rudiment is present. But the vacillating policy in the
matter of rudiments does not end here; for it is shown in a still more
aggravated form where within the limits of the same natural group of
organisms a rudiment is sometimes present and sometimes absent. For
instance, although in nearly all the numerous species of snakes there
are no vestiges of limbs, in the python we find very tiny rudiments of
the hind-limbs. (Fig. 8.) Now, is it a worthy conception of deity that,
while neglecting to maintain his unity of ideal in the case of nearly
all the numerous species of snakes, he should have added a tiny rudiment
in the case of the python--and even in that case should have maintained
his ideal very inefficiently, inasmuch as only two limbs, instead of
fou