136 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
appearing except in cases where their presence may be explained by 
the hypothesis of hereditary descent; while in thousands of such cases 
we find these structures undergoing every conceivable variety of 
adaptive modification. 
Consequently, special creationists must fall back upon another 
position and say,—Well, but it may have pleased the Deity to form 
a certain number of ideal types, and never to have allowed the 
structures occurring in one type to appear in any of the others. We 
answer,—Undoubtedly such may have been the case; but, if so, it is , 
a most unfortunate thing for your theory, because the fact implies 
that the Deity has planned his types in such a way as to suggest the 
counter-theory of descent. For instance, it would seem most capri- 
cious on the part of the Deity to have made the eyes of an innumerable 
number of fish on exactly the same ideal type, and then to have made 
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 have taken scrupulous care that in no one ideal particular, 
should the one type resemble the other. However, adopting for the 
sake of argument this great assumption, let us suppose that God did 
lay down these arbitrary rules for his own guidance in creation, and 
then let us see to what the assumption leads. If 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 efforts, so to speak, have been made to maintain the uniformity 
of type in the case of the fore-limb as previously explained, and should 
we not expect that in other and similar cases a similar method should 
have been followed? Yet we repeatedly find that this is not the case, 
Even in the whale, as we have seen, the hind-limbs are either alto- 
gether absent or dwindled almost to nothing; and it is impossible to see 
in what respects the hind-limbs are of any less ideal value than the 
fore-limbs—which are carefully preserved in all vertebrated animals 
except the snake, and the extinct Dinornis, where again we meet in 
this particular with a sudden and sublime indifference to the main- 
tenance of a typical structure (Fig. 15). Now say that if the theory 
of ideal types is true, we have in these facts evidence of a most unrea- 
sonable inconsistency. 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 
