370 REVIEWS—="ON THE ORIGIN OF SPECIES. 
“Tt may be asked how far I extend the doctrine of the modification of species. 
The question is difficult to answer, because the more distinct the forms are which 
we may consider, by so much the arguments fall away in force. But some 
arguments of the greatest weight extend very far.. All the members of whole 
classes can be connected together by chains of affinities, and all can be classified 
on the same principle, in groups subordinate to groups. Fossil remains some- 
times tend to fill up very wide intervaJs between existing orders. Organs in & 
rudimentary condition plainly show that an early progenitor had the organ in a 
fully developed state; and this in some instances necessarily implies an enormous 
amount of modification in the descendants. Throughout whole classes various 
structures are formed on the same pattern, and at ar embryonic age the species 
closely resemble each other. Therefore I cannot doubt that the theory of descent 
with modification embraces all the members of the same class. I believe that 
animals have descended from at most only four or five progenitors, and plants 
from an equal or lesser number, 
Analogy would lead me one step further, namely, to the belief that all animals 
and plauts have descended from some 2ne prototype. But analogy may be a 
deceitful guide. Nevertheless all living things have much in common, in their 
chemical composition, their germinal vesicles, their cellular structure, and their 
laws of growth and reproduction. We see this even in so trifling a circumstance 
as that the same poison often similarly affects plants and animals; or that the 
poison secreted by the gall-fly produces monstrous growths on the wild rose or 
oak-tree. Therefore I should infer from analogy that probably all the organic 
beings which have ever lived on this earth have descended from some one pri- 
mordial form, into which life was first breathed.” 
It is very clear, as already stated, that many of the so-called species 
of naturalists, are not true species, but simply varieties; and hence, 
arguments founded merely on closely related forms, are of compara- 
tively little weight as regards the main question here at issue. For 
the proper acceptation of the theory, it will be necessary to show the 
passage of one truly distinct type mto another, or of these into some 
common parent-type, so as to render an explanation of the structural 
homologies and other relations existing between them. If this cannot 
be effected by reference to existing Nature, let us look back into the 
rock-preserved annals of the Past, and see if these will lend us any 
aid. Mr. Darwin is forced to acknowledge that Geology fails, in this 
respect, to furnish any direct support to his hypothesis. But then, he 
argues, the geological record is incomplete. In place of a full and 
connected history, it offers to us only a few isolated leaves of the 
great book of the Past. Granting this, it must nevertheless be con- 
sidered highly adverse to his view—as he himself, indeed, has candidly 
stated—that in these stony annals we find everywhere the same unity 
