ake the eye of the octopus so exactly like these other eyes in
superficial appearance as to deceive so accomplished a naturalist as Mr.
Mivart, and yet to take scrupulous care that in no one ideal particular
should this solitary eye resemble all the host of other eyes. However,
adopting for the sake of argument this gigantic assumption, let us
suppose that God laid down these arbitrary rules for His own guidance in
creation, and let us see to what it leads. If, as is assumed, the Deity
formed a certain number of ideal types, and determined that on no
account should He allow any part of one type to appear in any part of
another, surely we should expect that within the limits of the same type
the same typical structures should always be present. Thus, remember
what desperate efforts, so to speak, there have been made to maintain
the uniformity of type in the case of the arm, and should we not expect
that in other and similar cases similar efforts should be made? Yet we
repeatedly find that this is not the case. Even in the whale, as we have
seen, the hind-limbs are not apparent; and it is impossible to see in
what respect the hind-limbs are of any less ideal value than the
fore-limbs, which, as we have also seen, are so carefully preserved in
nearly all vertebrated animals except the snakes, where again we meet in
this particular with a sudden and sublime indifference to the
maintenance of a typical structure. Now I say that if the theory of
ideal types is true, we have in these facts evidence of the most
unreasonable inconsistency; for no explanation can be assigned why so
much care should have been taken to maintain the type in some cases,
while such reckless indifference should have been displayed towards
maintaining it in others. 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 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--such as the absence of limbs--without
some of the other organs in the body 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 a long series of generations. And this combined testimony
of a number of organs in the same o