trees.
The Theory of Descent is to him an axiom of modern biology, though as a
matter of fact the circumstantial evidence in favour of it is extremely
fragmentary. The main arguments in favour of it appear to him to be the
general ones; the homologies and analogies revealed by comparative
morphology and physiology, the ascending series in the palaeontological
record, vestigial organs, parasitic degeneration, the origin of those
vital associations which we call consortism and symbiosis. These he
illustrates mainly by examples from his own special domain and personal
observation.

The simplest unicellular forms of life are to be thought of as at the
beginning of evolution; and, since mechanical causes cannot explain their
ascent, it must be assumed that they have an inherent "phylogenetic
potential of development," which, working epigenetically, results in
ascending evolution. He leaves us to choose between monophyletic and
polyphyletic evolution, but himself inclines towards the latter,
associating with it a rehabilitation of Wigand's theory of the primitive
cells. If, in the beginning, primitive forms of life arose (probably as
unicellulars) from the not-living, it is not obvious why we need think of
only one so arising, and, if many did so, why they should not have
inherent differences which would at once result in typically different
evolutionary series and groups of forms. But evolution does not go on _ad
libitum_ or _ad infinitum_, for the capacity for differentiation and
transformation gradually diminishes. The organisation passes from a labile
state of equilibrium to an increasingly stable state, and at many points
it may reach a terminus where it comes to a standstill. Man, the dog, the
horse, the cereals, and fruit trees appear to Reinke to have reached their
goal. The preliminary stages he calls "Phylembryos," because they bear to
the possible outcome of their evolution the same relation that the embryo
does to the perfect individual. Thus, _Phenacodus_ may be regarded as the
Phylembryo of the modern horse. It is quite conceivable that each of our
modern species may have had an independent series of Phylembryos reaching
back to the primitive cells. But the palaeontological record, and
especially its synthetic types, lead Reinke rather to assume that instead
of innumerable series, there have been branching genealogical trees, not
one, however, but several.

These views, together or separately, which are charac