In the first years of the study of “Entwickelungsmechanik” I pointed out that it must never be forgotten that the egg itself is the result of organogenesis. If, therefore, there are real mosaic-like specifications in some eggs at the beginning of cleavage, or during it, there may perhaps have been an *earlier* stage in the individual history of the egg which did not show such specifications of the morphogenetic structure. Two American authors share the merit of having proved this hypothesis. Conklin showed, several years ago, that certain intracellular migrations and rearrangements of material do happen in the first stages of ovogenesis in certain cases, but it is to E. B. Wilson[28] that science owes a proper and definitive elucidation of the whole subject. Wilson’s researches, pursued not only by descriptive methods,[29] but also by means of analytical experiment, led him to the highly important discovery that the eggs of several forms (nemertines, molluscs), which after maturation show the mosaic type of specification in their protoplasm to a more or less high degree, fail to show any kind of specification in the distribution of their potencies before maturation has occurred. In the mollusc egg a certain degree of specification is shown already before maturation, but nothing to be compared with what happens afterwards; in the egg of nemertines there is no specification at all in the unripe egg. [28] *Journ. Exp. Zool.* 1, 1904. [29] Great caution must be taken in attributing any specific morphogenetic part to differently coloured or constructed materials, which may be observed in the egg-protoplasm in certain cases. They may play such a part, but in other cases they certainly do not (see Lyon, *Arch. Entw. Mech.* 23, 1907). The final decision always depends on experiment. Maturation thus becomes a part of ontogeny itself; it is not with fertilisation that morphogenesis begins, there is a sort of ontogeny anterior to fertilisation. These words constitute a summary of Wilson’s researches. Taken together with the general results obtained about the potencies of the blastula and the gastrula of Echinus, they reduce what appeared to be differences of degree or even of kind in the specification of the egg-protoplasm *to mere differences in the time of the beginning of real morphogenesis*. What occurs in some eggs, as in those of Echinus, at the time of the definite formation of the germ layers, leading to a specification and restriction of their prospective potencies, may happen very much earlier in other eggs. But there exists in *every* sort of egg an *earliest* stage, in which all parts of its protoplasm are equal as to their prospectivity, and in which there are no potential diversities or restrictions of any kind. So much for differences in the *real material* organisation of the germ and their bearing on inequipotentialities of the cleavage cells. *The Intimate Structure of Protoplasm: Further Remarks*