The objection may be raised that in accepting Boveri’s facts and interpretation we pushed the miracle only one step farther and that we now have to explain the origin of the structure in the unfertilized egg. This Boveri has done by showing that the egg grows from the wall of the ovary and that that part of the egg which is connected with the wall of the ovary gives rise to the ectoderm layer, while the opposite part gives rise to the mesenchyme and the intestine. This shows a connection between the orientation of the egg in the wall of the ovary and its stratification. While this does not solve the problem of stratification in the egg it gives the clue to its solution. The ultimate origin of stratification probably goes back to the fact of the presence of watery and water-immiscible substances, such as fats. The experiments by Beutner and the writer have shown that the electromotive forces which are observed in living tissues originate at the boundaries between a watery and a water-immiscible phase, like oleic acid or lecithin.[125] In his earlier writings[126] the writer had thought that the colloids had special significance and this idea seems to prevail today; but the actual observations have shown that the phase boundary fat-water is of greater importance. Needless to say the fats if not present in the cell from the beginning can be formed in the metabolism. [125] Loeb, J., and Beutner, R., _Biochem. Ztschr._, 1912, xli., 1; xliv., 303; 1913, li., 288; li., 300; 1914, lix., 195. [126] Loeb, J., _The Dynamics of Living Matter_. New York, 1906. Introductory Remarks. 4. All the “regulation” in the egg is of a purely physicochemical character; it consists essentially of a flow of material. If this idea is correct, the apparent power of “regulation” of the blastomeres should differ according to the degree of fluidity and the possibility of different layers separating, and this assumption is apparently supported by facts. The first plane of segmentation of the egg is usually the plane of symmetry of the later organism and where the degree of fluidity is less than in the sea-urchin egg, a separation of the two first blastomeres should easily result in the formation of two half-embryos instead of two whole embryos.