This is the most recent and most valuable for general purposes of all books on the subject of heredity. No layman should express opinions on heredity or eugenics until he has read it, for it is extremely improbable that they will be valuable. Professor Thomson covers the whole ground with extreme lucidity and care and impartiality. The book is readable, nay more, fascinating from end to end, and it is liberally and usefully illustrated. It is the first general treatise on heredity which leads consciously, yet as of necessity, towards eugenics as the crown and goal of the whole study, and in this respect it undoubtedly marks an epoch. _The Methods and Scope of Genetics._ (1908.) By W. Bateson, M.A., F.R.S. This is the inaugural lecture, destined, I have little doubt, to become historic, which was delivered by Professor Bateson on his appointment to the new Darwin Chair of Biology at Cambridge. It is purposely included here for very good reasons. The reader who begins his serious study of heredity with Professor Thomson's work must be informed that though the author gives an interesting account of Mendelism, he is not a Mendelian, and neither his account of Mendelism nor his estimate of it is at all adequate for the present day. In truth there is the study of heredity before Mendelism and after, and though eugenics owes its modern origin to the founder of the school of biometrics, and though among his followers there are to be found many who decry and oppose the Mendelians, it is for the eugenist of single purpose to take the truth wherever it is to be found. It is now idle to deny either the general truth or the stupendous promise of Mendelism. Many vital phenomena besides heredity are studied by the statistical method, and are put down by it to heredity. The Mendelians take seeds of known origin, and plant them and note the result. They carry out experimental breeding not only amongst plants but amongst the higher animals, including mammals who, in all essentials of structure and function, are one with ourselves. It is not possible, I believe, to over-estimate the supreme importance of Mendelian enquiry for eugenics. Eugenics is founded upon heredity, and genetics, which is Professor Bateson's name for the physiology of heredity and variation, is now working at the very heart of those natural phenomena upon which eugenics depends. This lecture of Professor Bateson's is by the far the best introduction to Mendelism that exists, besides being the most recent and the most authoritative possible. With the lucidity of the born teacher (whose faculty, I have no doubt, is a Mendelian unit, not always inherited by the born observer) the author explains the essence of Mendelism. The usual expositor has not proceeded far upon his way before he is encumbering himself and the learner with the phenomena of dominance and recessiveness, which are not cardinal and are highly involved. Professor Bateson makes no allusion to them. But he gives an account