ect the germs
in the body by other agencies, and so produce inherited modifications
in the parent. [*] If this claim is sustained and enlarged, it may be
concluded that the greater changes of environment which we find in the
geological chronicle may have had a considerable influence of this kind.

* See a paper read by Professor Bourne to the Zoological
Section of the British Association, 1910. It must be
understood that when I speak of Weismannism I do not refer
to this whole theory of heredity, which, he acknowledges,
has few supporters. The Lamarckian view is represented in
Britain by Sir W. Turner and Professor Darwin. In other
countries it has a larger proportion of distinguished
supporters. On the whole subject see Professor J. A.
Thomson's "Heredity" (1909), Dewar and Finn's "Making of
Species" (1909--a Mendelian work), and, for essays by the
leaders of each school, "Darwinism and Modern Science"
(1909).

The general issue, however, must remain open. The Lamarckian and
Weismannist theories are rival interpretations of past events, and we
shall not find it necessary to press either. When the fish comes to
live on land, for instance, it develops a bony limb out of its fin. The
Lamarckian says that the throwing of the weight of the body on the main
stem of the fin strengthens it, as practice strengthens the boxer's arm,
and the effect is inherited and increased in each generation, until
at last the useless paddle of the fin dies away and the main stem
has become a stout, bony column. Weismann says that the individual
modification, by use in walking, is not inherited, but those young are
favoured which have at birth a variation in the strength of the stem of
the fin. As each of these interpretations is, and must remain, purely
theoretical, we will be content to tell the facts in such cases. But
these brief remarks will enable the reader to understand in what precise
sense the facts we record are open to controversy.

Let us return to the chronicle of the earth. We had reached the Devonian
age, when large continents, with great inland seas, existed in North
America, north-west Europe, and north Asia, probably connected by a
continent across the North Atlantic and the Arctic region. South America
and South Africa were emerging, and a continent was preparing to stretch
from Brazil, through South Africa and the Antarctic, to Australia and
India. The expans