62 Experimental Zoology 
Darwin’s provisional hypothesis of pangenesis. Many of the 
assumptions of this theory are scarcely in accord with our pres- 
ent cytological knowledge. For instance, few cytologists would 
be likely to admit that the germ-cells are built up of living par- 
ticles representing the different tissues and organs of the body 
that are collected by the reproductive organs. In a modified 
form, however, Darwin’s hypothesis could no doubt be brought 
up to date, if it were desirable to do so; but is it worth while to 
speculate further in this direction until we have a better basis 
of fact on which to rest the speculation; for, as has been pointed 
out, the experimental evidence in favor of the inheritance of 
acquired characters is unsatisfactory? 
The idea that the cell is made up of smaller morphological 
units that represent the various potentialities of the cell has been 
a favorite assumption of modern writers. Thus we have the 
physiological units of Spencer, the gemmules of Darwin, the 
pangens of de Vries, the plasomes of Wiesner, the micelle of 
Nageli, the plastidules of Haeckel, the biophores of Weismann, 
the biogens of Verworn, the idioblasts of Hertwig, etc. 
It is perhaps needless to point out that the kind of reasoning 
on which this method of treating the problem of heredity rests 
is of the sort that gives only the appearance of a real explanation, 
for the responsibility is only shifted to invisible and imaginary 
units that can be worked like puppets, at the will of the philoso- 
pher. Grossly ignorant as we are concerning the chemical and 
physical basis of cell activity, it is not probable that such guesses 
can be much more than fictions or at most symbolic. 
A single citation from Darwin will serve to bring the main 
points of his theory of pangenesis before us. ‘“‘It is universally 
admitted that the cells or units of the body increase by self-divi- 
sion or proliferation. . . . But besides this means of increase 
I assume that the units throw off minute granules which are 
dispensed throughout the whole system, that these, when sup- 
plied with proper nutriment, multiply by self-division, and are 
ultimately developed into units like those from which they were 
originally derived. These granules may be called gemmules. 
