IN this little monograph, Prof. Crew adds both to his own reputation as an exponent of his subject, and to the reputation of the admirable series of which it forms a part. Though his treatment is as clear as is humanly possible, he has been handicapped, like other writers in the series, by the extreme condensation that the size of the monograph demands. To have covered the whole subject of sex determination in 111 small pages of text (to which must be added 11 pages of bibliography, 5 pages of glossary, and author and subject indexes) would not have been possible with accuracy, had it been necessary to indulge in simplifying periphrases. As it stands, the book should prove an invaluable source of information and references both to those actually working in the field, and to those having to make occasional incursions into it.Sex Determination.Prof.F. A. E.CrewBy. (Methuen's Monographs on Biological Subjects.) Pp. ix + 138. (London: Methuen and Co., Ltd., 1933.) 3s. 6d. net.