To whatever cause it may be attributed, few writers whose intellectual activity has extended over so long a term of years as Mr. Spencer's have been so consistent in their utterances at different stages as he. The "Synthetic Philosophy" is the realization of a scheme of thought no less wonderful in its coherence and solidity than in its compass, the author having planted himself from the first at a point of view which gave him a clear command of his entire field. To say that no other system of thought equally comprehensive and equally coherent exists in the world to-day would be to make a statement which few competent and dispassionate authorities would deny. Notwithstanding this, there are writers not a few, particularly of the class "who write with ease," who, as we said at the outset, have a propensity for misunderstanding Mr. Spencer, and who consequently accuse him of inconsistencies and self-contradictions for which nothing that he has ever said affords any warrant. One of these gentlemen is the Duke of Argyll, who has lately offered the world another superfluous book under the title of Organic Evolution Cross-examined. The duke particularly concerns himself with Mr. Spencer's teaching in regard to the "survival of the fittest," and Mr. Spencer, in the columns of Nature, replies to him in a brief but sufficient manner. It is safe to say that Mr. Spencer's philosophy will show Cyclopean remains generations after the name of his ducal critic shall have passed forever into the mists of oblivion; and the "survival of the fittest" will thus be illustrated in a sense in which Mr. Spencer himself never used the words. Scientific Literature. SPECIAL BOOKS.