this stem-cell differs materially from the original ovum, both in
regard to form (morphologically), in regard to material composition
(chemically), and in regard to vital properties (physiologically). It
comes partly from the father and partly from the mother. Hence it is
not surprising that the child who is developed from it inherits from
both parents. The vital movements of each of these cells form a sum of
mechanical processes which in the last analysis are due to movements
of the smallest vital parts, or the molecules, of the living
substance. If we agree to call this active substance plasson, and its
molecules plastidules, we may say that the individual physiological
character of each of these cells is due to its molecular
plastidule-movement. HENCE, THE PLASTIDULE-MOVEMENT OF THE CYTULA IS
THE RESULTANT OF THE COMBINED PLASTIDULE-MOVEMENTS OF THE FEMALE OVUM
AND THE MALE SPERM-CELL.* (* The plasson of the stem-cell or cytula
may, from the anatomical point of view, be regarded as homogeneous and
structureless, like that of the monera. This is not inconsistent with
our hypothetical ascription to the plastidules (or molecules of the
plasson) of a complex molecular structure. The complexity of this is
the greater in proportion to the complexity of the organism that is
developed from it and the length of the chain of its ancestry, or to
the multitude of antecedent processes of heredity and adaptation.)


CHAPTER 1.8. THE GASTRAEA THEORY.

There is a substantial agreement throughout the animal world in the
first changes which follow the impregnation of the ovum and the
formation of the stem-cell; they begin in all cases with the
segmentation of the ovum and the formation of the germinal layers. The
only exception is found in the protozoa, the very lowest and simplest