192 
cant kind. If the germ-plasm is at all 
times distinct from the soma, then defi- 
nite characters acquired by the individ- 
ual in the course of its lifetime must 
perish with the individual. There was 
no known or conceivable mechanism by 
which such characters could be trans- 
ferred to the germ-cells and thus carried 
over to a succeeding generation. Weis- 
mann at once recognized this, and 
began that attack on the belief in the 
inheritance of acquired characters which 
furnished the sharpest post-Darwinian 
debate of the nineteenth century. Weis- 
mann argued in the following ways: 
(1) Such inheritance is theoretically in- 
conceivable; this argument was devel- 
oped in so thorough a fashion as to be 
regarded by many as conclusive in itself. 
(2) The data usually cited to support the 
case of the inheritance of acquired char- 
acters were shown to be so uncritical as 
not to bear examination, in some cases as 
to the facts themselves and in others as 
to their interpretation. Under the latter 
head the supposed inheritance of diseased 
conditions, as inferred at that time, was 
shown to be equally explicable on the 
assumption of inheritance of germinal 
weakness. (38) Weismann carried out 
detailed critical experiments to investi- 
gate the commonly accepted idea of 
inheritance of mutilations; for many 
generations he amputated the tails of 
white mice and found by measurement 
that the tails came as long at the end as 
at the beginning. (4) He argued suc- 
cessfully against the contention that 
inheritance of acquired characters is 
necessary to explain evolution. 
If heritable variations do not arise by 
use or disuse of parts or by action of 
incident external forces upon the organ- 
ism, it is necessary to explain how they 
come about. Weismann put forward 
three ideas which contain the germ of our 
modern working hypotheses, viz. (1) 
THE AMERICAN MUSEUM JOURNAL 
the theory of germinal selection; (2) 
the results of amphimixis; and (3) 
direct action of environment on the 
germ. 
The theory of germinal selection in- 
volves the postulated architecture of the 
germ-plasm, which was conceived as 
composed of a great number of elemen- 
tary particles (determinants), each the 
representative of some unit-character of 
the organism. Weismann reasoned in 
general that conditions in the germ- 
plasm must be conceived as variable, 
and thus more or less favorable for the 
growth of these elements; favored ones 
would tend to increase, those in unfavor- 
The concep- 
tion of the struggle for existence was 
able positions to decrease. 
transferred to the germ-plasm and varia- 
tion-producing modifications of the germ- 
This 
Weismann himself 
laid great store, has been sterile; it was 
plasm were attributed thereto. 
theory, by which 
purely formal and has had no effect on 
research. 
The second hypothesis concerning the 
effects of amphimixis, or admixture of 
parental germ-plasms in fertilization, was 
by no means original with Weismann; 
but he was the first one adequately to 
prove its significance and to show how 
the admixture of different sets of paren- 
tal characteristics, their shuffling in the 
filial germ-plasm and redistribution in 
the half reduction divisions of the filial 
germ-cells is a constant, and perhaps 
the greatest, source of heritable varia- 
tions. However, he did not proceed 
quite to the extreme of the past presi- 
dent of the British Association for the 
Advancement of Science, Professor Bate- 
son, and postulate the possibility that 
evolution has been productive of nothing 
essentially new from its inception. 
The third source of heritable varia- 
tions postulated by Weismann, viz. 
the action of incident external forces 
