by comparing them
with the mature stages of lower organisms, since we regard them as forms
inherited from ancestors belonging to such lower stages"[382] (p. 6).

It is worth noting that in Gegenbaur's opinion comparative anatomy was
prior in importance to embryology, that embryology could hardly exist as
an independent science, since it must seek the interpretation of its
facts always in the facts of comparative anatomy (_Grundzuege_, pp. 7-8).

While Gegenbaur was at one with all "pure" morphologists, whether
evolutionary or pre-evolutionary, in minimising as far as possible the
importance of function in the study of form, he was too cautious and
sober a thinker not to recognise the immense part which function really
plays. Thus he classified organs, according to their function, into
those that established relations with the external world and those that
had to do with nutrition and reproduction, very much as Bichat had done
before him.

Like Darwin, Haeckel and most evolutionists, he interpreted the
homological resemblances of animals as being due to heredity, their
differences as due to adaptation,[383] but he did not adopt Haeckel's
crude and shallow definition of these terms. For Gegenbaur heredity was
a convenient expression for the fact of transmission, and was not
explained offhand as the mere mechanical result of a certain material
structure handed down from germ to germ. Adaptation he defined in a way
which took the fullest account of function, and was as far as possible
removed from Haeckel's definition of it as the direct mechanical effect
of the environment upon the organism. "The organism is altered," writes
Gegenbaur, "according to the conditions which influence it. The
consequent _Adaptations_ are to be regarded as gradual, but steadily
progressive, changes in the organisation, which are striven after during
the individual life of the organism, preserved by transmission in a
series of generations, and further developed by means of natural
selection. What has been gained by the ancestor becomes the heritage of
the descendant. Adaptation and Transmission are thus alternately
effective, the former representing the modifying, the latter the
conservative principle.... Adaptation is commenced by a change in the
function of organs, so that the _physiological relations_ of organs play
the most important part in it. Since adaptation is merely the material
expression of this change of function, the modification