vary, now in a
favourable, now in an unfavourable direction. If a female produces
eggs, which contain favourably varying determinants in the worker-ids,
then these eggs will give rise to workers modified in the favourable
direction, and if this happens with many females, the colony concerned
will contain a better kind of worker than other colonies.

I digress here in order to give an account of the intimate processes,
which, according to my view, take place within the germ-plasm, and
which I have called "_germinal selection_." These processes are of
importance since they form the roots of variation, which in its turn
is the root of natural selection. I cannot here do more than give a
brief outline of the theory in order to show how the Darwin-Wallace
theory of selection has gained support from it.

With others, I regard the minimal amount of substance which is
contained within the nucleus of the germ-cells, in the form of rods,
bands, or granules, as the _germ-substance_ or _germ-plasm_, and I
call the individual granules _ids_. There is always a multiplicity of
such ids present in the nucleus, either occurring individually, or
united in the form of rods or bands (chromosomes). Each id contains
the primary constituents of a _whole_ individual, so that several ids
are concerned in the development of a new individual.

In every being of complex structure thousands of primary constituents
must go to make up a single id; these I call _determinants_, and I
mean by this name very small individual particles, far below the
limits of microscopic visibility, vital units which feed, grow, and
multiply by division. These determinants control the parts of the
developing embryo,--in what manner need not here concern us. The
determinants differ among themselves, those of a muscle are
differently constituted from those of a nerve-cell or a glandular
cell, etc., and every determinant is in its turn made up of minute
vital units, which I call _biophores_, or the bearers of life.
According to my view, these determinants not only assimilate, like
every other living unit, but they _vary_ in the course of their
growth, as every living unit does; they may vary qualitatively if the
elements of which they are composed vary, they may grow and divide
more or less rapidly, and their variations give rise to
_corresponding_ variations of the organ, cell, or cell-group which
they determine. That they are undergoing ceaseless fluctuations in
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