progressive transformation which evidently correspond with the
differences of different mammalian orders and families."[377]

The biogenetic law went beyond both the Meckel-Serres law and the law of
von Baer in that it recognised that the ancestral history of the species
accounts in part for the course which the development of the individual
takes, that in a certain sense, though not in the crude way supposed by
Haeckel, phylogeny is the cause of ontogeny. This thought, that the
organism is before all an historical being, is of course implied in the
evolution idea, is indeed the essential core of it. Take away this
element from the biogenetic law--not a difficult matter--and it becomes
merely a law of idealistic morphology, applicable to evolution
considered as an ideal process, as the progressive development in the
Divine thought of archetypal models.

As a book, the _General Morphology_ suffers a good deal from the arid,
schematic, almost scholastic manner of exposition adopted. Haeckel's
Prussian mania for organisation, for absolute distinctions, for
iron-bound formalism, is here given full scope. A treatment less
adequate to the variety, fluidity and changeableness of living things
could hardly be imagined.

His doctrine, though it remains essentially unchanged, receives in his
later works a less formal and more concrete expression, and, in
particular, his views on the biogenetic law undergo some small
modification.

Even in the _General Morphology_ Haeckel had recognised that ontogeny is
neither a complete nor an entirely accurate recapitulation of phylogeny;
he had admitted, following F. Mueller, that the true course of
recapitulation was frequently modified by larval and foetal adaptations.
As time went on, he was forced to hedge more and more on this point, and
finally in his _Anthropogenie_ (1874) and his second paper on the
Gastraea theory (1875),[378] he had to work out a distinction between
palingenetic and cenogenetic characters, of which much use was made by
subsequent writers.

The distinction may be given in Haeckel's own words:--"Those ontogenetic
processes," he writes, "which are to be referred immediately, in
accordance with the biogenetic law, to an earlier completely developed
_independent ancestral form_, and are transmitted from this by
_heredity_, obviously possess _primary_ importance for the understanding
of the casual-physiological relations; on the other hand, those
developmental proc