divisions, etc.

To form the somatoplasm of the different tissues of the body, this
complicated organization breaks up, as the egg divides, into an
ever-increasing number of cells. First, so to speak, the corps
separate to preside over the formation of different body regions.
Then the different divisions, brigades, and regiments, composing
each next higher unit, separate, being detailed to form ever
smaller portions of the body. The process of changing germ-plasm
into somatoplasm is one of disintegration. The germ-plasm
contains representatives of the whole army; a somatic cell only
representatives of one special arm of a special training. Germ-plasm
in the egg is like Humpty-Dumpty on the wall; somatoplasm, like
Humpty-Dumpty after his great fall.

I use these rude illustrations to make clear one point: Germ-plasm
can easily change into somatoplasm, but somatoplasm once formed can
never be reconverted into germ-plasm, any more than the fallen hero
of the nursery rhyme could ever be restored.

The germ-plasm is, according to Weismann, a very peculiar, complex,
stable substance, continuous from generation to generation since the
first appearance of life on the globe. It is in the body of the
parent, but scarcely of it. Its relation to the body is like that of
a plant to the soil or of a parasite to its host. It receives from
the body practically only transport and nourishment. It is like a
self-perpetuating, close corporation; and the somatoplasm has no
means of either controlling it or of gaining representation in it.

Says Weismann[A]: "The germ-cells are contained in the organism, and
the external influences which affect them are intimately connected
with the state of the organism in which they lie hid. If it be well
nourished, the germ-cells will have abundant nutriment; and,
conversely, if it be weak and sickly, the germ-cells will be
arrested in their growth. It is even possible that the effects of
these influences may be more specialized; that is to say, they may
act only upon certain parts of the germ-cells. But this is indeed
very different from believing that the changes of the organism which
result from external stimuli can be transmitted to the germ-cells
and will redevelop in the next generation at the same time as that
at which they arose in the parent, and in the same part of the
organism."

[Footnote A: Essays upon Heredity, p. 105.]

But if the germ-plasm has this constitution and relation to