ASPECTS AND ETIOLOGY OF CARCINOMA 55
a fern or flowering-plant. In the line from egg to egg there are two generations—an asexual form, and one which, as it is the bearer of sexual organs, is spoken of as the sexual generation. Under prevailing views of development the line of ancestry from generation to generation is exceedingly simple—too simple, indeed, to explain the facts ; so simple that Nature could not adopt it in practice, were she to make the trial. It may be represented thus egg → embryo or sexual generation → egg → embryo, etc., the egg producing the embryo; the latter, when mature, forming from its own tissues new eggs. This is, undoubtedly, one of the most impossible conceptions which ever formed part of a science. The amended cycle of development and the course of heredity are as follow: egg → trophoblast (phorozoon or bearing animal, asexual generation) → primitive germ-cell → primary germ-cells → secondary germ-cells → gametes, eggs or sperms → fertilized egg.* In the line of ancestry, as given here, a line which, apart from the asexual generation, is one of unicellular organisms, the embryo finds no place. It arises from one of the primary germ-cells, whose number is always a definite one—2, 4, 8, 16, 32, etc.—and the rest enter the embryonic body to form its sexual products. A more detailed account of this cycle will be found in “Heredity and the Epicycle of the Germ-Cells.” The four important items in the cycle are : (1) The gametes, egg and sperm, by whose union, to form a zygote, a new cycle is initiated; (2) the first product of the zygote, the phorozoon, trophoblast, or asexual generation; (3) the primary germ-cells, destined for future generations; and (4), only important to enable the completion of the cycle, the embryo or sexual generation.
Any and every primary germ-cell, if it develop or unfold
* See Fig. 5, Chapter V.