THE title of this little volume of four lectures delivered at Princeton University is likely to cause some disappointment. The book is almost entirely an exposition of certain facts as to in heritance ascertained by experiments with the fruit-fly, Drosophila ampelophila, and “a review of a long series of researches as to the nature o the hereditary material.” The author claims that “the mechanism of heredity has been discovered” and that “the problem of heredity has been solved.” He holds that “the mechanism of the chromosomes offers a satisfactory solutiOn of the traditional problem of heredity.” A Critique of the Theory of Evolution. By Prof. T. H. Morgan. Pp. x + 197. (Princeton: University Press; London: Oxford University Press, 1916.) Price 6s. net.