FOUNDATION OF A THEORY OF HEREDITY. 193 



propagation takes place, and thus the original stage of the germ is 

 reached.' 



Hence, according to Nageli, the different stages of ontogeny arise 

 out of the activities of different parts of the idioplasm : certain 

 groups of micellae in the idioplasm represent the germs (' Anlageii ') 

 of certain structures in the organism : when any such germ reacts 

 under stimulation it produces the corresponding structure. It seems 

 to me that this hypothesis bears some resemblance to Darwin's 

 theory of pangenesis. I think that Nageli's preformed germs of 

 structures (' Anlagen ') and his groups of such germs are highly 

 elaborated equivalents of the gemmules of pangenesis, which, 

 according to Darwin, manifest activity when their turn comes, or, 

 according to Nageli, when they react under stimulation. When a 

 group of such germs, by their active growth or by their 'irritation,' 

 have caused a similar active growth or a similar irritation in the 

 next group, the former may come to rest, or may remain in a 

 state of activity together with its successor, for a longer or 

 shorter period. Its activity may even last for an unlimited time, 

 a,s is the case in the formation of leafy shoots in many plants.' 



Here, again, we recognize the fact that Nageli's whole hypothesis 

 is intimately connected with the supposition that the entire mass 

 of idioplasm is continuous throughout the organism. Sometimes 

 one part of the idioplasm and sometimes another part is irritated, 

 and then produces the corresponding organ. But if, on the other 

 hand, the idioplasm does not represent a directly continuous mass, 

 but is composed of thousands of single nucleoplasms which only 

 act together through the medium of their cell-bodies, then we 

 must substitute the conception of ' ontogenetic stages of develop- 

 ment of the idioplasm ' for the conception of germs of structure 

 (' Anlagen '). The different varieties of nucleoplasm which arise 

 during ontogeny represent, as it were, the germs of Nageli (' An- 

 lagen '), because, by means of their molecular structure, they create 

 a specific constitution in the cell-bodies over which they have 

 control, and also because they determine the succession of future 

 nuclei and cells. 



It is in this sense, and no other, that I can speak of the presence 

 of preformed germs (' Anlagen ') in the idioplasm. We may sup- 

 pose that the idioplasm of the first segmentation nucleus is but 

 slightly different from that of the second ontogenetic stage, viz. 



