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 palæontological 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 characterised chiefly by the catch-words “polyphyletic descent,” “labile and stable equilibrium,” and so on, crop up together or separately in the writings of various evolutionists belonging to the opposition wing. They are usually associated with a denial of the theory of natural selection, and with theories of “Orthogenesis,” “Heterogenesis,” and “Epigenesis.” We shall discuss them later when we are considering the factors in evolution. But we must first take notice of a work in which the theories opposed to Darwinian orthodoxy have been most decisively and aggressively set forth. As far back as 1892 O. Hamann, then a lecturer on zoology in Göttingen, gathered these together and brought them into the field, against Haeckel in particular, in his book “Entwicklungslehre und Darwinismus.”(27)