ising homogeny other than the well-worn methods
generally employed in the search after homologies.

There was a close spiritual affinity between the speculative
evolutionists and the transcendentalists. Both showed the same
subconscious craving for simplicist conceptions--the transcendentalists
clung fast to the notion of the absolute unity of type, of the ideal
existence of the "one animal," and the evolutionists did precisely the
same thing when they blindly and instinctively accepted the doctrine of
the monophyletic descent of all animals from one primeval form. Geoffroy
persisted in regarding Arthropods as being built on the same plan as
Vertebrates: Dohrn and Semper did nothing different when they derived
both groups from an ancestor combining the main characters of both. The
determination to link together all the main phyla of the animal kingdom
and to force them all into a single mould was common to evolutionary and
pre-evolutionary transcendentalists alike.

From the fact that all Metazoa develop from an ovum which is a simple
cell, the evolutionists inferred that all must have arisen from one
primordial cell. From the fact that the next step in development is the
segmentation of the ovum, they argued that the ancestral Metazoa came
into being through the division of the primal Protozoon with aggregation
of the division-products. From the fact that a gastrula stage is very
commonly formed when segmentation has been completed, they assumed that
all germ-layered animals were descended from an ancestral Gastraea.

They quite ignored the possibility that a different explanation of the
facts might be given; they seized upon the simplest and most obvious
solution because it satisfied their overwhelming desire for
simplification. But is the simplest explanation always the
truest--especially when dealing with living things? One may be permitted
to doubt it. It is easy to account for the structural resemblance of the
members of a classificatory group, by the assumption that they are all
descended from a common ancestral form; it is easy to postulate any
number of hypothetical generalised types; but in the absence of positive
evidence, such simplicist explanations must always remain doubtful. The
evolutionists, however, had no such scruples.

Phylogenetic method differed in no way from transcendental--except
perhaps that it had learnt from von Baer and from Darwin to give more
weight to embryology. The criticisms passe