Fifth and last, I should like to gather under the head of morphophysics a number of researches, nearly all of which are very recent, and which tackle the doctrine of the chemical and physical causes of development. These researches have been largely experimental in character, and though we are only at the beginning of this sort of work, yet the results already obtained are of the highest value and make us hope for far greater results to come.
There should be added logically a sixth heading for the physiology of the embryo, but so little has been done and so little is doing in this part of biology that only in the future can this logically correct sixth division correspond to a field of active research. Here poverty of achievement makes further present consideration by us superfluous.
It is unnecessary to argue in order to prove to you that the study of generation is of importance to the medical man. The results which embryologists have already offered in solving some of the problems of generation form part of the stock in trade of every practitioner, for every one must know something of the uterus and placenta, must know that there is no communication between the fœtal and maternal circulation—no passage of the blood from the mother to that of the child: that there is no machinery for the making of so-called maternal impressions; that conception depends primarily upon the fusion of two living elements, the ovum and spermatazoon, which arise as living and integral parts of the parental bodies, and must know thus that there is a continuity of life, an earthly immortality, and that from generation to generation life is uninterrupted. All these notions and many others derived from embryology are now-a-days part and parcel of every physician's information, and it is hard to realize that a short time ago many of these facts were unknown to us. I believe that in the course of the next few years many new discoveries concerning generation will be made which will in their turn become familiar to all. I expect especially in regard to the subject of heredity a great increase in our knowledge, because the subject has attracted many investigators and some notable results have already been achieved. I may instance the history of the germ cells in which I have been especially interested. Professor Moritz Nussbaum on the basis of certain observations which he had made, put forward in 1880 the theory of germinal continuity. He pointed out that there is noteworthy evidence in the development of various animals tending to show that the germinal cells from which the sexual products arise are separated off very early from the other cells of the embryo and undergo very little alteration until the time comes for them to be transformed into sexual elements, male or female, as the case may be. Dr. F. A. Woods, working in my laboratory upon the embryos of dog-fish brought the first conclusive demonstration that Nussbaum's theory is true for a vertebrate. He found that the germ cells are set apart, have a distinct
