We would urge in conclusion that the study is well worth while, even for those to whom it has a non-professional interest. It should be sufficiently obvious to any earnest thinker that the problems which are involved in the study of embryology are precisely those which are of the very greatest importance to humanity at large. With this subject is most intimately bound up that of heredity itself, which has been dealt with in another volume of this series. No true understanding of what can be done, or what should be done, in the direction of improving the lot of generations to come, or of making the most of the generation at present existent, can be obtained by any who are absolutely ignorant of these topics. It is only by their study that we realise that the human embryo, which is to become the human individual, consists, to a very large extent, of characters and features which are unalterably settled for it beforehand, to which nothing can be added, and from which nothing can be taken away. In other words, the possibilities for any individual are those which are pre-existent in the germ-plasm from which he or she originates. These possibilities, however, depend upon the environment in which the embryo, infant, child, and adult is subsequently placed for their full expansion. In many directions the inherited tendencies transmitted by the continuity of germ-plasm are unalterably and strictly defined. In many other directions these inherited tendencies can be so modified, drawn out, or even partially suppressed, by suitable surroundings of a hygienic, educative, and moral nature, that if the process be taken in hand sufficiently early wonderful successes may result. These results are those for which the social reformer and the philanthropist and the serious student of sociology are earnestly striving, but it is only by a study of the sciences of Heredity and Embryology that accurate data can be obtained from which justifiable conclusions may be drawn. The great fact which embryology teaches is that the past is unfolded stage by stage, with certain omissions and additions, so that in very truth-- "The softest dimple in a baby's smile Springs from the whole of past eternity, Taxed all the sum of things to bring it there." BIBLIOGRAPHY The following books will be found to deal in detail with some of the general questions in the foregoing pages:-- _The Laws of Heredity_. By G. Archdall Reid, M.B., F.R.S.E. (London. Methuen.) This great work should be read by all who are interested in the subject of Heredity and all the problems involved in it. It deals in an exhaustive and interesting manner with the characteristics of living beings, the method of development, the function of sex, the present evolution of man, and kindred topics.