237 
ON THE ANIMALS WHICH AKE MOST NEARLY IN- 
TERMEDIATE BETWEEN BIRDS AND REPTILES.^ 
HOSE who hold the doctrine of Evolution (and I am one of 
them) conceive that there are grounds for believing that the 
world, with all that is in it and on it, did not come into existence 
in the condition in which we now see it, nor in anything ap- 
proaching that condition. On the contrary, they hold that the 
present conformation and composition of the earth’s crust, the 
distribution of land and water, and the infinitely diversified 
forms of animals and plants which constitute the present popu- 
‘lation of the globe, are merely the final terms in an immense 
series of changes which have been brought about, in the course 
of immeasurable time, by the operation of causes more or less 
similar to those which are at work at the present day. 
Perhaps this doctrine of Evolution is not maintained con- 
sciously and in its logical integrity by a very great number of 
persons.! But many hold, particular applications of it without - 
committing themselves to the whole ; and many, on the other 
hand, favour the general doctrine without giving an absolute 
assent to its particular applications. Thus, one who adopts the 
nebular hypothesis in Astronomy, or is a Uniformitarian in 
Geology, or a Darwinian in Biology, is, so far, an adherent of 
the doctrine of Evolution. And, as I can testify from personal 
experience, it is possible to have a complete faith in the general 
doctrine of Evolution and yet to hesitate in accepting the 
Nebular, or the Uniformitarian, or the Darwinian hypotheses 
in all their integrity and fulness. For many of the objections 
* A Lecture delivered before the Royal Institution of Great Britain on 
February 7, 1868. 
t The only complete and systematic statement of the doctrine with which 
I am acquainted is that contained in Mr. Herbert Spencer’s System of 
Philosophy ; ” a work which should be carefully studied by all who desire 
to know whither scientific thought is tending. The volumes at present 
published are entitled, “First Principles,” and “Principles of Biology.” 
VOL. VII. — NO. XXVIII. * S 
By Pkofessor Huxley, LL.D., F.R.S. 
