debates a change has been brought by Weismann's
challenge for evidence that use and disuse have any transmitted
effects at all. Hitherto the transmission of many acquired
characteristics had seemed to most naturalists so obvious as not to
call for demonstration.[65] Weismann's demand for facts in support of
the main proposition revealed at once that none having real cogency
could be produced. The time-honoured examples were easily shown to be
capable of different explanations. A few certainly remain which cannot
be so summarily dismissed, but--though it is manifestly impossible
here to do justice to such a subject--I think no one will dispute that
these residual and doubtful phenomena, whatever be their true nature,
are not of a kind to help us much in the interpretation of any of
those complex cases of adaptation which on the hypothesis of unguided
Natural Selection are especially difficult to understand. Use and
disuse were invoked expressly to help us over these hard places; but
whatever changes can be induced in offspring by direct treatment of
the parents, they are not of a kind to encourage hope of real
assistance from that quarter. It is not to be denied that through the
collapse of this second line of argument the Selection hypothesis has
had to take an increased and perilous burden. Various ways of meeting
the difficulty have been proposed, but these mostly resolve themselves
into improbable attempts to expand or magnify the powers of Natural
Selection.

Weismann's interpellation, though negative in purpose, has had a
lasting and beneficial effect, for through his thorough demolition of
the old loose and distracting notions of inherited experience, the
ground has been cleared for the construction of a true knowledge of
heredity based on experimental fact.

In another way he made a contribution of a more positive character,
for his elaborate speculations as to the genetic meaning of
cytological appearances have led to a minute investigation of the
visible phenomena occurring in those cell-divisions by which
germ-cells arise. Though the particular views he advocated have very
largely proved incompatible with the observed facts of heredity, yet
we must acknowledge that it was chiefly through the stimulus of
Weismann's ideas that those advances in cytology were made; and though
the doctrine of the continuity of germ-plasm cannot be maintained in
the form originally propounded, it is in the main true and
illumin