"The central idea of Professor Giddings's Principles of Sociology, a work that has the honor of being the first independent attempt in English to treat of sociology as such, is that we must postulate on the part of human beings what he calls a _consciousness of kind_. Critics of his volume have naturally told him that this is essentially a philosophical idea, found in Hegel and in British ethical writers of the eighteenth century." We quote the above from an article by Professor Caldwell, entitled Philosophy and the Newer Sociology, in the October Contemporary. We are not prepared to dispute Professor Caldwell's statement that the idea of the "consciousness of kind" may be found in the writers to whom he refers; but it would have been very much to the point if he had mentioned that it is to be found most clearly enunciated in Mr. Herbert Spencer's Principles of Sociology. In an article contributed to this magazine in December, 1896, Mr. Spencer took occasion to point out that what Professor Giddings seemed to regard as an _aperçu_ peculiar to himself had been distinctly formulated years before in his own writings. In proof of this he quoted the following passages: "Sociality having thus commenced, and survival of the fittest tending ever to maintain and increase it, it will be further strengthened by the inherited effects of habit. _The perception of kindred beings, perpetually seen, heard, and smelt, will come to form a predominant part of consciousness-_-so predominant that absence of it will inevitably cause discomfort." "Among creatures led step by step into gregariousness, there will little by little be established a pleasure in being together--a pleasure in the consciousness of one another's presence--a pleasure simpler than, and quite distinct from, those higher ones which it makes possible." The fact is that there is much more in Spencer than most recent writers have ever explored; and the newer sociologists would do well, before putting forward claims to originality, to make sure that they have not been anticipated by the veteran philosopher. Scientific Literature. SPECIAL BOOKS. In _The Play of Animals_[59] we are offered a book upon an essentially new topic; for, although much has been written concerning the habits and intelligence of animals, no special consideration has been given to their play or its psychic significance. The survey of this virgin territory seems to the critical reader to have disclosed such limitless area to Professor Groos that he fails to indicate its legitimate boundaries. He confesses himself overcome by a sense of its vastness, stating that the "versatility needed for a thorough investigation is so comprehensive that it is unattainable by an ordinary mortal."