very questionable whether a
roughness of the skin, or minute processes, would be useful to a {39}
swimming animal; the motion of which they would as much impede as aid,
unless they were at once capable of a suitable and appropriate action,
which is against the hypothesis. Again, the change from mere indefinite and
accidental processes to two regular pairs of symmetrical limbs, as the
result of merely fortuitous, favouring variations, is a step the
feasibility of which hardly commends itself to the reason, seeing the very
different positions assumed by the ventral fins in different fishes. If the
above suggestion made in opposition to the views here asserted be true,
then the general constancy of position of the limbs of vertebrata may be
considered as due to the position assumed by the primitive rugosities from
which those limbs were generated. Clearly only two pairs of rugosities were
so preserved and developed, and all limbs (on this view) are descendants of
the same two pairs, as all have so similar a fundamental structure. Yet we
find in many fishes the pair of fins, which correspond to the hinder limbs
of other animals, placed so far forwards as to be either on the same level
with, or actually in front of, the normally anterior pair of limbs; and
such fishes are from this circumstance called "thoracic," or "jugular"
fishes respectively, as the weaver fishes and the cod. This is a wonderful
contrast to the fixity of position of vertebrate limbs generally. If then
such a change can have taken place in the comparatively short time occupied
by the evolution of these special fish forms, we might certainly expect
other and far more bizarre structures would (did not some law forbid) have
been developed, from other rugosities, in the manifold exigencies of the
multitudinous organisms which must (on the Darwinian hypothesis) have been
gradually evolved during the enormous period intervening between the first
appearance of vertebrate life and the present day. Yet, with these
exceptions, the position of the limbs is constant from the lower fishes up
to man, there being always an anterior pectoral pair placed in front of a
posterior or pelvic pair when both are present, and in no single {40}
instance are there more than these two pairs.

[Illustration: MOUTH OF A WHALE.]

The development of whalebone (baleen) in the mouth of the whale is another
difficulty. A whale's mouth is furnished with very numerous horny plat