433 
DARWINISM 
CHAP. 
although it is very difficult to make them intelligible to persons 
unfamiliar with the main facts of modern embryology. 1 
The problem is thus stated by Weismann : “ How is it 
that in the case of all higher animals and plants a single cell 
is able to separate itself from amongst the millions of most 
various kinds of which an organism is composed, and by 
division and complicated differentiation to reconstruct a new 
individual with marvellous likeness, unchanged in many cases 
even throughout whole geological periods 1 ” Darwin at¬ 
tempted to solve the problem by his theory of “Pangenesis,” 
which supposed that every individual cell in the body gave off 
gemmules or germs capable of reproducing themselves, and that 
portions of these germs of each of the almost infinite number of 
cells permeate the whole body and become collected in the 
generative cells, and are thus able to reproduce the whole 
organism. This theory is felt to be so ponderously complex 
and difficult that it has met with no general acceptance among 
physiologists. 
The fact that the germ-cells do reproduce with wonderful 
accuracy not only the general characters of the species, but 
many of the individual characteristics of the parents or more 
remote ancestors, and that this process is continued from 
generation to generation, can be accounted for, Weismann 
thinks, only on two suppositions which are physiologically 
possible. Either the substance of the parent germ-cell, after 
passing through a cycle of changes required for the construction 
of a new individual, possesses the capability of producing anew 
germ-cells identical with those from which that individual was 
developed, or the new germ-cells arise , as far as their essential 
and characteristic substance is concerned, not at all out of the body 
of the individual, but direct from the parent germ-cell. This latter 
view Weismann holds to be the correct one, and, on this theory, 
heredity depends on the fact that a substance of special mole¬ 
cular composition passes over from one generation to another. 
This is the “ germ-plasm,” the power of which to develop itself 
into a perfect organism depends on the extraordinary complica¬ 
tion of its minutest structure. At every new birth a portion 
1 The outline here given is derived from two articles in Nature, vol. 
xxxiii. p. 154, and vol. xxxiv. p. 629, in which Weismann’s papers are summar¬ 
ised and partly translated. 
