from what has been said, that in this case EVERYTHING depends on the
fluctuations of the elements of the germ-plasm. Germinal selection, here
as elsewhere, presents the variations of the determinants, and personal
selection favours or rejects these, or,--if it be a question of organs
which have become useless,--it does not come into play at all, and allows
the descending variation free course.

It is obvious that even the problem of COADAPTATION IN STERILE ANIMALS can
thus be satisfactorily explained. If the determinants are oscillating
upwards and downwards in continual fluctuation, and varying more
pronouncedly now in one direction now in the other, useful variations of
every determinant will continually present themselves anew, and may, in the
course of generations, be combined with one another in various ways. But
there is one character of the determinants that greatly facilitates this
complex process of selection, that, after a certain limit has been reached,
they go on varying in the same direction. From this it follows that
development along a path once struck out may proceed without the continual
intervention of personal selection. This factor only operates, so to
speak, at the beginning, when it selects the determinants which are varying
in the right direction, and again at the end, when it is necessary to put a
check upon further variation. In addition to this, enormously long periods
have been available for all these adaptations, as the very gradual
transition stages between females and workers in many species plainly show,
and thus this process of transformation loses the marvellous and mysterious
character that seemed at the first glance to invest it, and takes rank,
without any straining, among the other processes of selection. It seems to
me that, from the facts that sterile animal forms can adapt themselves to
new vital functions, their superfluous parts degenerate, and the parts more
used adapt themselves in an ascending direction, those less used in a
descending direction, we must draw the conclusion that harmonious