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 micellae 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. 



