Morphology. 59 
typical structures modified so as to perform very 
different functions, we never find any of these 
particular types of structure in other large branches 
of the tree. That is to say, we never find typical 
structures 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 capricious 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 
