To us the present revival of the derivative hypothesis,in a more winning shape than it ever before had,was not unexpected. We wonder that any thoughtful observer of the course of investigation and of speculation in science should not have foreseen it, and have learned at length to take its inevitable coming patiently; the more so, as in Darwins treatise it comes in a purely scientific form, addressed only to scientifi men. The notoriety and wide popular perusal of this treatise appear to have astonished the author even more than the book itself has astonished the reading world Coming as the new presentation does from a naturalist of acknowledged character and ability and marked by a conscientiousness and candor which have not always been reciprocated we have thought it simply right to set forth the doctrine as fairly and as favorably as we could There are plenty to decry it and the whole theory is widely exposed to attack For the arguments on the other side we may look to the numerous adverse publications which Darwin s volume has already called out and especially to those reviews which propose directly to refute it. Taking various lines and reflecting very diverse modes of thought, these hostile critics may be expected to concentrate and enforce the principal objections which can be brought to bear against the derivative hypothesis in general, and Darwins new exposition of it in particular.