rganism 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.[1]

[1] This consideration is, I believe, original. Several exceptions to
its validity might be adduced, but as a general principle it certainly
holds good.

I will now briefly touch on another branch of the argument from
morphology--the argument, namely, from rudimentary structures.

Throughout the animal and vegetable kingdoms we constantly meet with
organs which are the dwarfed and useless representatives of organs
which, in other and allied kinds of animals and plants, are of large
size and functional utility. Thus, for instance, the unborn whale has
rudimentary teeth, which are never destined to cut the gums; and we all
know that our own rudimentary tail is of no practical service. Now,
rudimentary organs of this kind are of such common occurrence, that
almost every species presents one or more of them. The question,
therefore, is--How are they to be accounted for? Of course the theory of
descent with adaptive modification has a delightfully simple answer to
supply, viz., that when, from changed conditions of life, an organ which
was previously useful becomes useless, natural selection, combined with
disuse and so-called economy of growth, will cause it to dwindle till it
becomes a rudiment. 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 is
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 so extraordinary a method is 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
realised. 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, if
possible, in a more aggravated form where, within the limits of the same
natural group of organisms, a rudiment is sometimes present and
sometimes absent. For instance, to take again the case of limbs, in