AUGUST WEISMANN 
particles into cells like those from which 
they originally arose. The inheritance 
of acquired characters could thus be 
explained on the assumption that modi- 
fied cells produced modified gemmules 
which reproduced the acquired modifica- 
tion in the succeeding generation. 
Weismann rejected the centripetal 
part of the Darwinian theory, while still 
retaining certain fundamental concep- 
tions of pangenesis. The theory of the 
continuity of the germ-plasm however 
offers a complete antithesis to Darwin’s 
theory in the sense that, whereas Darwin 
regarded the germ-cells as a secretion of 
the entire body, Weismann regarded 
them as genetically distinct from all the 
remainder of the body or soma — as 
producing the soma but not produced by 
it. In the production of the soma not all 
of the active protoplasm (germ-plasm) 
of the original germ-cell was used up; 
but a certain amount of it was retained 
unmodified and formed the germ-cells 
of the new generation. Thus the germ 
cells of any one generation were regarded 
as a direct unmodified product of the 
germ-cells of the parents, and so were 
handed down from generation to genera- 
tion, essentially uninfluenced by the 
soma, retaining their original attributes 
and developmental capacities unchanged. 
This conception constituted an immense 
simplification of the Darwinian scheme. 
However, Weismann accomplished 
Darwin’s theory had been 
a purely imaginative construction and 
was frankly acknowledged by himself 
to be a formal hypothesis. Weismann’s 
theory on the other hand was based on 
the newly discovered facts concerning cell 
division, the fertilization of the egg and 
the processes involved in the origin of 
germ-cells. As a theory of heredity it 
has precisely the same relation to Dar- 
win’s theory of pangenesis that the 
latter’s theory of natural selection had 
much more. 
191 
borne to preceding evolution theories. 
It permitted test and verification and 
involved predictions which have been 
verified in certain cases, the most crucial 
test of any theory. 
The studies of cell-division carried out 
by Fleming, Hertwig and others had 
revealed a precise set of phenomena in 
nuclear division common to animals and 
plants, which suggested (Roux) a funda- 
mental réle of the nuclear elements or 
chromosomes in the cell life. Similarly 
the studies of Hertwig, Strasburger, Fol, 
and Van Beneden on fertilization had 
shown the predominantly — significant 
part played in the process by the nucleus 
and its chromosomes; and the begin- 
nings of knowledge, destined soon to be 
carried very much farther, concerning 
the maturation phenomena of the germ- 
cells, had demonstrated a similar pre- 
dominance of significance of the chromo- 
somes in these processes. Weismann 
used all of these data first in the identi- 
fication of the chromosomes as the really 
significant part of the germ-cells (germ- 
plasm), and second in the construction 
of a detailed theory on this basis. He 
was thus able to predict as a logical 
necessity, the occurrence at some stage 
in the life history of a reduction division 
of the nuclei of the germ-cells which 
would halve the number of chromosomes 
instead of maintaining the whole number 
as in all of the other divisions. This 
prediction has been universally realized 
in plants and animals. The phenome- 
non was later found to parallel exactly 
the Mendelian laws of inheritance and to 
furnish their explanation to a consider- 
able extent. There are few instances 
in the history of science, outside of 
astronomy, in which prediction has been 
so adequately and significantly fulfilled. 
The fundamental assumption of the 
theory of continuity of the germ-plasm 
involved corollaries of the most signifi- 
