can
almost certainly be demonstrated, and his results go far to support the
conception of the organism, referred to above, as a combination or
mosaic of independently inherited features.

It was said at the beginning of this sketch that most of the more
notable lines of advance in Biology could be traced back to the impetus
given by the acceptance of the theory of Evolution, and the desire to
test and prove that theory in every biological field. It is most
convenient, therefore, to take this root-idea as a starting-point, and
to see how the various branches of study have diverged from it and have
themselves branched out in various ways, and how these branches have
often again become intertwined and united in the later development of
the science.

Perhaps the most obvious method of testing the theory of evolution is by
the study of fossil forms, and our knowledge of these has progressed
enormously during the period under review. Not only have a number of new
and strange types of ancient life come to light, but in some cases, e.g.
in that of the horse and elephant, a very complete series of
evolutionary stages has been discovered. In this branch, however, as in
almost all others, the results have not exactly fulfilled the
expectations of the early enthusiasts. On the one hand, evolution has
been shown to be a much more complex thing than at first seemed
probable; and on the other, many of the gaps which it was most hoped to
fill still remain. A number of most remarkable 'missing links' have been
discovered, such as, for example, _Archaeopteryx_, the stepping-stone
between the Reptiles and the Birds, and the faith of the palaeontologist
in the truth of evolution is everywhere confirmed. But the hope of
finding all the stages, especially in the ancestry of Man, has not been
realized, and it has been found that what at one time were regarded as
direct ancestors are collaterals, and that the problem of human
evolution is much less simple than was once supposed.

A second important piece of evidence in favour of evolution is provided
by the study of the geographical distribution of animals, on which much
work was done in the earlier part of the period under review. And in
this connexion mention must be made of the science of Oceanography, for
our whole knowledge of life in the abysses of the ocean, and almost all
that we know of the conditions of life in the sea in general, has been
gained in the last fifty years.

Anoth