AUGUST WEISMANN 
upon the germ-plasm directly was never 
adequately analyzed by him. He al- 
ludes to it in his earlier essays, without 
following the matter farther. It has 
required the detailed investigations of 
Tower and MacDougal especially to give 
this real meaning, and such studies are 
still in their infancy. However, it is 
important to recognize Weismann’s fore- 
sight with reference to this. 
It is no part of this review to point out 
the weaknesses of Weismann’s theories, 
for this is not the place for an adequate 
critical review. However, we should 
be open to the charge at least of incom- 
pleteness if we failed to point out that 
Weismann’s theories were based on the 
data of a purely morphological period 
of genetic research. The experimental 
studies which followed close on the heels 
of his fundamental publications swept 
away, probably irrecoverably, some of 
the elements of his conceptions. Genetic 
conceptions are coming to be more and 
more physiological; and it is a logical 
necessity that analysis should continue 
to proceed in this direction. Biologists 
generally have discarded the Weisman- 
nian notion of living independent en- 
tities (determiners) in the germ-plasm, 
representative of entire unit characters, 
and have replaced it by the conception 
195 
of differential (chemical) factors located 
in the germ-plasm and interacting with 
other factors (or chemical substances) 
in the cell. But when we effect such a 
change of conceptions, fundamental as 
it may be, we still deal to a considerable 
extent with those phenomena of the 
chromosomes whose significance Weis- 
mann did so much to make plain. Simi- 
larly we can no longer deal with the 
development of the individual in terms 
of qualitative nuclear analysis as Weis- 
mann did, for it has been proved that the 
cytoplasm has a predominant determin- 
ing influence in many of the phenomena 
at least, and it has not been proved that 
nuclei in general grow qualitatively dif- 
ferent. However, it must be realized 
that Weismann’s precise formulation of 
his theory of individual development 
furnished the stimulus for some of the 
fundamental investigations that have 
made real advances in this difficult field. 
I think it is fair to say that Weismann 
played as important a part in the devel- 
opment of a theory of heredity as Dar- 
win did in the theory of evolution in 
general; he must, therefore, be regarded 
as among the greatest of Darwin’s fol- 
lowers and supporters. The biological 
world must forever hold his memory in 
reverence. 
