ociety,
1865."_)]

Another instance which may be cited is the asymmetrical condition of the
heads of the flat-fishes (Pleuronectidae), such as the sole, the flounder,
the brill, the turbot, &c. In all these fishes the two eyes, which in the
young are situated as usual one on each side, come to be placed, in the
adult, both on the same side of the head. If this condition had appeared at
once, if in the hypothetically fortunate common ancestor of these fishes an
eye had suddenly become thus transferred, then the perpetuation of such a
transformation by the action of "Natural Selection" is conceivable enough.
Such sudden changes, however, are not those favoured by the Darwinian
theory, and indeed the accidental occurrence of such a spontaneous
transformation is hardly conceivable. But if this is not so, if the transit
was gradual, then how such transit of one eye a minute fraction of the {38}
journey towards the other side of the head could benefit the individual is
indeed far from clear. It seems, even, that such an incipient
transformation must rather have been injurious. Another point with regard
to these flat-fishes is that they appear to be in all probability of recent
origin--_i.e._ geologically speaking. There is, of course, no great stress
to be laid on the mere absence of their remains from the secondary strata,
nevertheless that absence is noteworthy, seeing that existing fish
families, _e.g._ sharks (Squalidae), have been found abundantly even down so
far as the carboniferous rocks, and traces of them in the Upper Silurian.

Another difficulty seems to be the first formation of the limbs of the
higher animals. The lowest Vertebrata[34] are perfectly limbless, and if,
as most Darwinians would probably assume, the primeval vertebrate creature
was also apodal, how are the preservation and development of the first
rudiments of limbs to be accounted for--such rudiments being, on the
hypothesis in question, infinitesimal and functionless?

In reply to this it has been suggested that a mere flattening of the end of
the body has been useful, such, _e.g._, as we see in sea-snakes,[35] which
may be the rudiment of a tail formed strictly to aid in swimming. Also that
a mere _roughness_ of the skin might be useful to a swimming animal by
holding the water better, that thus minute processes might be selected and
preserved, and that, in the same way, these might be gradually increased
into limbs. But it is, to say the least,