Weismann laid hold of this idea, but transmuted it to fit in with his original theory of the germplasm. Shortly put, his view is as follows: The whole of the nuclear material is not hereditary material, but only a definite part is such, and this part, throughout the development of the individual, remains unaltered in composition, and finally becomes the starting-point for the generations to come. The remaining and greater part of the nuclear material does not remain in an unaltered condition. The layers of cells, first formed in the embryo, grow unlike each other, and give rise to different organs and tissues; Weismann draws the inference that the nuclear substance as well alters during the process of development, transforming itself in a regular, orderly fashion, until, finally, each different kind of cell in the whole body contains a specific nuclearplasm. This segregation and transformation begins with the process of cleavage itself, and thus 'the two daughter-cells that arise from the first cleavage of the egg-cell become different, so that the one contains all the hereditary characters for the ectoderm, the other for the endoderm. In further course the ectodermal nuclearplasm divides into that containing the primary germs of the nervous system, and that containing the similar constituents for the outer skin. By further cellular and nuclear divisions the inherited germs for the nervous system separate into those for the sense organs, those for the central nervous system, and so forth, until there are separated the germs for all the separate organs, and for the production of the minutest histological differentiation.' Weismann calls the diverging nuclearplasms into which the primitive germplasm is gradually transformed _histogenous_, because they determine the specific characters of the tissues. He assumes that the primitive, original germplasm has a most complicated molecular structure, while the histogenous nuclearplasms for tissue-cells, like muscle-cells, nerve-cells, sense-cells, gland-cells, and so forth, have relatively simpler structures. As, during the growth of the embryo, the germplasm becomes transformed into the histogenous plasms, its molecular structure becomes simpler in proportion to the fewer different possibilities of development each separated portion of it comes to contain.