394 REVIEWS—ON THE ORIGIN OF SPECIES. 
only with their mutual relations as parts of the great system of the 
UNIVETSL. © 
Lut us now turn to Mr. Huxley’s mode of dealing with the subject 
before us, and we shall first quote a passage containing his statement 
of the principles upon which such inguiries as that proposed must be 
conducted (Lecture VI., p. 130, American edition.) 
“] stated to you in substance, if notin words, that wherever there are com- 
plex masses of phenomena to be inquired into, whether they be phenomena of 
the affairs of daily life, or whether they belong to the more abstruse and difficult 
problems laid before the philosopher, our course of proceeding in unravelling 
that complex chain of phenomena with a view to get at its cause, is always the 
same; in all cases we must invent a hypothesis ; we must place before ourselves 
some more or less likely supposition respecting that cause; and then, having 
assumed a hypothesis, having supposed a cause for the phenomena in question, 
Wwe must endeavour, on the one hand, to demonstrate our hypothesis, or, on the 
other, to upset and reject it altogether by testing it in three ways. We must, 
in the first place, be prepared to prove that the supposed causes of the phe- 
nomena exist in nature; that they are what the logicians call vere cauwse—true 
causes ;—in the next place, we should be prepared to show that the assumed 
causes of the phenomena are competent to produce such phenomena as those 
which we wish to explain by them; and in the last place, we ought to be able 
to show that no other known causes are competent to produce these phenomena. 
If we can succeed in satisfying these three conditions, we shall have demon- 
strated our hypothesis; or rather I ought to say, we shall have proved it as far 
as certainty is possible for us ; for, after all, there is no one of our surest convic- 
tions which may not be upset, or at any rate modified by a further accession of 
knowledge.” 
We make no objection to these principles, but, as already indicated, 
we consider it as requiring proof that the phenomena of species are 
such as demand any investigation of their cause, or easily admit 
the supposition of any second cause. We pass on to Professor Hux- 
ley’s concise statement of the Darwinian hypothesis (Lect. VI., p. 
131, Am. Ed.) 
“What is Mr. Darwin’s hypothesis? As I apprehend it—for I have put it into 
a shape more convenient for common purposes than J could find verbatim in his 
book—as I apprehend it, I say, it is, that all the phenomena of organic nature, 
past and present, result from, or are caused by, the inter-action of those proper- 
ties of organic matter, which we have called Aravism and VARIABILITY, with 
the ConpiT1ons oF ExisTENcE; or in other words,—given the existence of organic 
matter, its tendency to transmit its properties, and its tendency occasionally to 
vary; and, lastly, given the conditions of existence by which organic matter is 
surrounded—that these put together are the causes of the Present and of the 
Past conditions of Organic Naturs.” 
