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.