( Ixi ) 
standing. The conditions of speculation in the two great 
departments of natural science which have been under 
consideration are not exactly the same, and the differences 
in the method of treatment must not be lost sight of. If in 
the physical sciences there is, to use the expression of the 
late Prof. Stanley Jevons, "unbounded license of theorising," 
it is because we can appeal to Nature so readily by the 
experimental method and get our answer one way or the 
other, by imposing rigid conditions which are under our 
control. In the biological sciences this is not the case ; all 
who are acquainted with experimental work in biology know 
how difficult it is, generally, to get definite answers to our 
questions — the conditions are vastly more complex when we 
come to deal with living organisms. I remember once 
remarking to the late Mr. Darwin how difficult it was to get 
Nature to give a definite answer to a simple question, and 
he replied with a flash of humour: "She will tell you a 
direct lie if she can." The practical result of this difference 
is that the speculation of an hour may take a lifetime for its 
verification. But I see no reason why, on these grounds, we 
should repress the spirit of speculation. If, as our former 
President says, it is given to few to be able to speculate with 
advantage — and in this I thoroughly agree with him — it is 
our paramount duty for the present and future welfare of our 
science, to give every man's honest thought our most serious 
attention, and to encourage the faculty whenever and wherever 
we find it, as the most precious means of advancing scientific 
knowledge. The "bugbear" is a very harmless animal 
if you look him boldly in the face, and if you treat him gently 
and put him into harness, he will drive the chariot of science 
for you at a speed that will leave the empirical method far 
behind in the race for the knowledge of Nature's ways. 
The great service which the founders of the modern doc- 
trine of Evolution have rendered to science has, in my belief, 
been not only the particular theory of species transformation 
with which their names will ever be associated, but the im- 
portation into biology of the methods of the physical sciences. 
Writing to Wallace, in 1857, Darwin said : "I am a firm 
believer that without speculation there is no good and original 
