It seems to us that a question of this character does not admit of a satisfactory solution, and this opinion will be shared by all who have considered the idea of physical identity. It is a notion obscure, uncertain, and full of contradictions. We have formed it because it answers our practical needs. But it is certainly evident that it corresponds to no well defined external phenomenon. In fact, we understand by physical identity the constant reunion of certain elements in a certain order. If the order of these elements is very slightly modified, or if a very small number of these elements is replaced by others, we do not hesitate to say that the physical identity in question has not been altered by these insignificant modifications. If, on the other hand, the order has been almost totally destroyed, if the greater portion of the elements has been renewed, we should, on the contrary, say that the identity of the thing in question had been lost in these alterations and that a new object had replaced the old. Replace a stone in a house and the latter remains the same house; rebuild the house upon a new plan and with different materials retaining very little of the first construction, and it is a different house. But between these two extreme cases there is a whole series of possible intermediate changes, and we are not able to establish clearly by any exterior mark the point where physical identity ends. This is a matter of personal estimation; I might even say of caprice; and all the discussions raised upon these questions appear to me wholly idle. I believe, accordingly, that the thesis of Weismann regarding the immortality of Infusoria eludes a direct refutation. It is neither confirmed nor overturned by observed facts. ALFRED BINET. ON THE MATERIAL RELATIONS OF SEX IN HUMAN SOCIETY. Much interest is displayed at present in the development of woman, both as to her personal characteristics, and in her relations to her surroundings in human society. It is justly said that the civilisation of a nation may be measured by the degree of humanity displayed by its men towards its women. This is for the reason that, since women are the weaker sex, man has only ethical reasons for self-restraint in his treatment of her. Nowhere is the sex-interest under better ethical control than in the United States; and it is in this country also that we hear the most of reforms which are necessary in order that woman may attain a further development, and assume a higher position in relation to the state. This being the case, it is extremely important that the foundation facts, or in other words the necessary natural conditions, under which the sexes co-operate in society, should be fully understood. That they are not understood, or that they are intentionally ignored in some quarters, is evident to any one who reads the current literature of the subject.