Unite in the process of fertilisation to form the fertilised ovum, which divides a given number of times and forms daughter-cells, which are germ-cells; one of which, and one only, goes on dividing to form the body-cells, and so produces the new individual, which as it grows includes in itself those cells (germ-cells) previously formed. The rest are germ-cells, which subsequently form the eggs and sperms of the new individual, _i.e._ they are the germ-cells of the next generation. They cannot develop independently, but when they unite with the egg or sperm of another individual, a new fertilised ovum is formed and the cycle begins again. This is a startling thought, but it is one which a moment's careful consideration will show is the only conceivable explanation of all the facts of physical continuity. Once it is grasped a flood of light is thrown upon the whole science of Embryology. The individual is seen to be literally a "chip of the old block," and the "old block" means the whole sequence of germ-cells which has preceded his formation. In the light of this fact it is obvious why like produces like; indeed, it is obvious that it must do so. Further, we now understand at once that since one generation of germ-cells directly produces those of the next, there is no reason in the world why an individual should not more nearly resemble a remote ancestor than his own immediate parents. As a simple matter of fact this frequently happens. He does so because the germ-cell from which he sprang is composed of protoplasm handed down in direct continuity by successive generations of germ-cells from time immemorial. In fact the problem in the light of this evidence is not so much--as it always seems to the writer--to understand why children resemble parents and ancestors, as to understand how it is that they do not resemble them more. There is no difficulty now in explaining the fundamental propositions with which we started, namely, that children resemble their parents. There is no difficulty in the understanding why a child resembles not only its immediate parents, but even its ancestors. There is even no difficulty in understanding why a child should resemble its ancestors, even though it does not resemble its parents. Given the simple truth that the germ-plasm is continuous from one generation to another, all these things become as clear as daylight.