he present
day; they might or might not be discoverable as fossils. That they had
real existence either now or at some past epoch Haeckel never doubted.
In his construction of phylogenetic trees he was so confident in the
truth of his biogenetic law that he largely disregarded and consistently
minimised the importance of the evidence from palaeontology.

The biogenetic law differed from the Meckel-Serres law chiefly in the
circumstance that many of the adult lower forms whose organisation was
supposed to be repeated in the development of the higher animals were
purely hypothetical, being deduced directly from a study of ontogeny and
systematic relationships. The hypothetical ancestral forms which the
theory thus postulated naturally took their place in the natural system,
for they were merely the concrete projections or archetypes of the
classificatory groups.

The transcendentalists, of course, conceived evolution, whether real or
ideal, as a uniserial process, whereas Haeckel conceived it as
multiserial and divergent. It is here that the superficial agreement of
the biogenetic law with the law of von Baer comes in.

We might almost sum up the relation of the biogenetic law to the laws of
von Baer and Meckel-Serres by saying that it was the Meckel-Serres law
applied to the divergent differentiation upheld by von Baer instead of
to the uniserial progression believed in by the transcendentalists.

How near in practice Haeckel's law came to the recapitulation theory of
the transcendentalists may be seen in passages like the following, with
its partial recognition of the _Echelle_ idea:[276]--"As so high and
complicated an organism as that of man ... rises upwards from a simple
cellular state, and as it progresses in its differentiating and
perfecting, it passes through the same series of transformations which
its animal progenitors have passed through, during immense spaces of
time, inconceivable ages ago.... Certain very early and low stages in
the development of man, and other vertebrate animals in general,
correspond completely in many points of structure with conditions which
last for life in the lower fishes. The next phase which follows on this
presents us with a change of the fish-like being into a kind of
amphibious animal. At a later period the mammal, with its special
characteristics, develops out of the amphibian, and we can clearly see,
in the successive stages of its later development, a series of steps of