least
the merit that they give a vivid impression of what is most plausible and
attractive in the idea of descent, and moreover they have helped towards
orientation in the discussion. Nor can we ignore the very marked taxonomic
and architectonic talent which their construction displays.

Weismann's Evolutionist Position.

The most characteristic representative, however, of the modern school of
unified and purified Darwinism is not Haeckel, but the Freiburg zoologist,
Weismann. Through a long series of writings he has carried on the conflict
against heterodox, and especially Lamarckian theories of evolution, and
has developed his theories of heredity and the causes of variation, of the
non-transmissibility of acquired characters, and the all-sufficiency of
natural selection. In his latest great work, in two volumes, "Lectures on
the Theory of Descent,"(11) he has definitely summed up and systematised
his views. These will interest us when we come to inquire into the problem
of the factors operative in evolution. For the moment we are only
concerned with his attitude to the Theory of Descent as such. It is
precisely the same as Haeckel's, although he is opposed to Haeckel in
regard to the strictly Darwinian standpoint. The Theory of Descent has
conquered, and it may be said with assurance, for ever. That is the firm
conviction on which the whole work is based, and it is really rather
treated as a self-evident axiom than as a statement to be proved. Weismann
takes little trouble to prove it. All the well-known, usually very clear
proofs from palaeontology, comparative anatomy, &c., which we are
accustomed to meet with in evolutionist books are wanting here, the
genealogical trees of the Equidae, with the gradually diminishing number of
toes and the varying teeth, of _Planorbis multiformis_, of the ammonites,
the graduated series of stages exhibited by individual organs, for
instance, from the ganglion merely sensitive to light up to the intricate
eye, or from the rayed skeleton of the paired fins in fishes up to the
five-fingered hands and feet of the higher vertebrates, &c. These are only
briefly touched upon in the terse "Introduction," and the whole of the
comprehensive work is then directed to showing what factors can have been
operative, and to proving that they must have been "Darwinian" (selection
in the struggle for existence), and not Lamarckian or any other. This is
shown in regard to the coloration of a