quickly or slowly, how regularly or irregularly they change. Nor do we
know how far a determinant must be strengthened by the passive flow of the
nutritive stream if it is to be beyond the danger of unfavourable
variations, or how far it must be weakened passively before it loses the
power of recovering itself by its own strength. It is no more possible to
bring forward actual proofs in this case than it was in regard to the
selection-value of the initial stages of an adaptation. But if we consider
that all heritable variations must have their roots in the germ-plasm, and
further, that when personal selection does not intervene, that is to say,
in the case of parts which have become useless, a degeneration of the part,
and therefore also of its determinant must inevitably take place; then we
must conclude that processes such as I have assumed are running their
course within the germ-plasm, and we can do this with as much certainty as
we were able to infer, from the phenomena of adaptation, the selection-
value of their initial stages. The fact of the degeneration of disused
parts seems to me to afford irrefutable proof that the fluctuations within
the germ-plasm ARE THE REAL ROOT OF ALL HEREDITARY VARIATION, and the
preliminary condition for the occurrence of the Darwin-Wallace factor of
selection. Germinal selection supplies the stones out of which personal
selection builds her temples and palaces: ADAPTATIONS. The importance for
the theory of the process of degeneration of disused parts cannot be over-
estimated, especially when it occurs in sterile animal forms, where we are
free from the doubt as to the alleged LAMARCKIAN FACTOR which is apt to
confuse our ideas in regard to other cases.

If we regard the variation of the many determinants concerned in the
transformation of the female into the sterile worker as having come about
through the gradual transformation of the ids into worker-ids, we shall see
that the germ-plasm of the sexual ants must contain three kinds of ids,
male, female, and worker ids, or if the workers have diverged into soldiers