While, however, these things are said at the outset, as affording commencement for the study of an evolution theory, and delivering us from the supposition that there is an inevitable antagonism between science and recognition of the supernatural, we revert to the ruling principle for this whole inquiry, that science must prosecute its own researches, unfettered by forecast of consequences; and that the Bible is not to be handled as if it were a book of science, for it neither lays restraints upon human inquiry, nor delivers us from the need for it. The best method for entering upon a study of the theory of evolution by natural selection is to take Mr. Darwin's own account of the manner in which it began to take shape before his mind. In his "historical sketch of the recent progress of opinion on the origin of species,"[BB] he traces to Lamark the first suggestions on the subject, directing public attention to the question in 1801; thereafter a succession of naturalists including St. Hilaire, Wells, and Patrick Matthew, from separate and incidental observations, dwelt upon the difficulty of distinguishing species, and on the evidence of an archetypal idea, or common plan of structure, being applicable in the history of whole orders. Mr. Darwin then gives the following biographical references at the outset,--"When on board H. M. S. 'Beagle,' as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to throw some light on the origin of species--that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions which then seemed to me probable: from that period to the present day I have steadily pursued the same object."[BC] Such is Mr. Darwin's opening paragraph in the now celebrated _Origin of Species_. No one interested in such investigations will hesitate to approve and trust the "patiently accumulating and reflecting on all sorts of facts;" nor can there be any hesitation in granting the warrantableness of his beginning to speculate as to the probable results. On the other hand, even the most ardent admirers of the evolution theory can not refuse to allow that only its principles are certain, while its ultimate form is still matter of conjecture and speculation. Quite divergent lines of speculation have found a start within the compass of the phenomena brought under review, and it is already apparent that opposite tendencies of thought have