Another question of much importance in connection with our present topic is the part played by the individual cells in the early development of the whole egg, or of any part of the egg. Hertwig (’93) thinks that the development is brought about by the action of the individual cells on each other. Driesch, when he states that the fate of a blastomere is a function of its position in the whole, does not commit himself definitely one way or the other so far as the cell as a unit is concerned. Whitman and others have urged the insufficiency of the cell theory, and think that cell boundaries play no important part in the development, but that the embryo develops as a whole. This has seemed to me to be the more probable view in the light of certain results of experimental embryology. Driesch, in later papers, has also opposed Hertwig’s idea, and Wilson in his book on _The Cell_ has also, to a certain extent, adopted this point of view. The formation of a typical larva in the sea-urchin and in amphioxus out of one-half or one-fourth the whole number of cells demonstrates, I think, the insufficiency of the cell-unit hypothesis. The discovery of continuous protoplasmic connections between neighboring cells, and the formation of new protoplasmic connections between all regions, as found by Mrs. G. F. Andrews,[129] gives us a basis of fact on which to rest the hypothesis of the embryo being a whole structure. This view meets with no great difficulty on the grounds that the nuclei are distinct centres of metabolic activity, for we know at present so little of what sort of action takes place between the nucleus and the protoplasm that we cannot rest our argument on any demonstrable relation.