The Presidential Address. 83
edition, as also in his 'Antiquity of Man,' he not only gave a
masterly exposition of the Darwinian theory, but added
considerably to its weight, and enforced its acceptance by
several new and striking lines of argument.
It would lead me too far astray on this occasion were I to
attempt to go in any detail over the various lines of evidence
converging upon the central idea of evolution. It suffices to
say that many large groups of biological facts that had before
appeared isolated and inexplicable were not only in the
strictest scientific sense explained, but "as by the stroke of
the enchanter's wand" the various great subdivisions of
Biology fell into, and became part of, Darwin's scheme of
Nature. "Every ray is gathered into one focus, and the rich
development of theory guides the apparently most remote
phenomena of organic life into the stream of proof."25 Let
us consider, for instance, the generalised facts of Embryology.
The development of an organism from the first germ to the
mature state is essentially a process of evolution. The
researches of embryologists, beginning with the illustrious
Karl Ernst von Baer, and ending alas! in recent times with
the lamented Francis Maitland Balfour, have shown that in
the course of its individual development an animal passes
through stages which approximate it at first to the lowest
types, and then in succession to types of increasing spe-
cialisation. The individual in fact "rises in organisation"
in the same sense as does the species. Specialisation increases
with development, till finally the adult animal acquires all
the characters of the species to which it belongs. How are
such facts intelligible if we reject the theory of descent ?
The researches of Darwin upon the laws of inheritance have
shown that all characters tend to be transmitted by parents
to their offspring at the same age or a little earlier than they
appear in the parents. This is Haeckel's law of "homo-
chronic heredity." The embryonic phases of an organism
are thus reminiscences of its past development—recapitula-
tions of the stages through which its ancestors passed in the
course of their evolution. The individual development or
25 Lange, I. c, vol. iii., p. 31,