ale" (p. 112). Evolution takes place as the environment allows,
and in a sense in opposition to the environment.

He believed in saltatory evolution, for he considered that the lower
oviparous Vertebrates could not be transformed into birds by slow
modification, but only by a sudden transformation of their lungs, which
would bring about the other characteristics of birds (p. 80). He
considered, too, that transformations could arise by means of monstrous
development (p. 86). In this connection the experiments which he made on
the hen's egg[103] in order to produce artificial monstrosities are
significant, though his purpose was rather to obtain proof of the
inadequacy of the preformation hypothesis.[104]

It seems probable enough that if Geoffroy had developed his views on
evolution he would finally have been led to interpret unity of plan in
terms of genetic relationship. But as it was he remained at his
morphological standpoint. He did not interpret rudimentary organs as
useless heritages of the past; he preferred to think that Nature had
prepared double means for the same function, one or other being
predominant according as the animal lived in the water or on the land.
"To the animal that lives exclusively in the air Nature has granted an
organisation suited to this mode of respiration, without however
suppressing the other corresponding means, that is to say, without
depriving it of a second system which is applicable only to the mode of
respiration by the intermediary of water, and _vice versa_."[105]

He seems, in one instance at least, to have hit upon the root-idea of
the biogenetic law, but he was far from appreciating its significance.
He recognised that an amphibian in its development passed through a
stage when it was in all essentials similar to a fish, and he saw in
this visible transformation a picture of the evolutionary
transformation. "An amphibian," he writes,[106] "is at first a fish under
the name of tadpole, and then a reptile [_sic_] under that of frog....
In this observed fact is realised what we have above represented as an
hypothesis, the transformation of one organic stage into the stage
immediately superior." But it is not clear that he considered the
development of the amphibian to be a _repetition_ of its ancestral
history.

He went, however, a certain length towards recognising the main
principle of a law which was a commonplace of German transcendental
thought, and was developed later