40 Darwin, and after Darwin. 
Thus, for instance, ‘‘nothing can be easier than to 
define a number of characters common to all birds; 
but with crustaceans any such definition has hitherto 
been found impossible. There are crustaceans at the 
opposite ends of the series, which have hardly a 
character in common; yet the species at both ends, 
from being plainly allied to others, and these to others, 
and so onwards, can be recognised as unequivocally 
belonging to this, and to no other class of the arti- 
culata'” Now it is evident that this progressive 
modification of specific types—-where it cannot be 
said that the continuity of resemblance is anywhere 
broken, and yet terminates in modification so great 
that but for the connecting links no one could divine 
a natural relationship between the extreme members 
of the series,—it is evident that such chains of af- 
finity speak most strongly in favour of a transmutation 
of the species concerned, while it is impossible to 
suggest any explanation of the fact in terms of the 
rival theory. Tor if all the links of such a chain 
were separately forged by as many acts of special 
creation, we can see no reason why B should re- 
semble A, C resemble B, and so on, but with ever 
slight though accumulating differences, until there is 
no resemblance at all between A and Z. 
I hope enough has now been said to show that all 
the general principles and particular facts appertaining 
to the natural classification of plants and animals, are 
precisely what they ought to be according to the 
theory of genetic descent; while no one of them is 
such as might be—and, indeed, used to be—expected 
1 Origin of Species, pp. 368-9. 
