48 THE DOCTRINE OE IMMORTALITY 



themselves but also in part at least in an influence exerted by 

 the rest of the body. In the case of polyembryony, the rudi- 

 ment, or anlage, possesses the capacity of forming aU tissues 

 and organs. During regeneration also, which in many animals 

 may go very far, we see that the complete structure is produced 

 anew and we recognize here again the phenomenon which we 

 call regulation. The physiological explanation of regulation 

 we do not yet possess, although we have learned already a 

 little concerning it. 



The sexual propagation plays a greater role than the 

 asexual, and is often the exclusive method of progagation, 

 especially in the higher plants and animals. We learned in 

 yesterday's lecture that the cells of the animal body dif- 

 ferentiate themselves, that is to say, that their protoplasm 

 acquires new qualities and that their power of division 

 diminishes. Differentiated cells are not suited for propaga- 

 tion. If it should occur that aU the cells of an animal or a 

 plant shoidd pass through a complete cytomorphosis, they 

 would aU die off, the organism would reach its end, and could 

 produce no progeny. As a matter of fact, however, all the 

 ceUs do not become differentiated. Of the undifferentiated 

 cells, the necessary number in each species is reserved for 

 the formation of the sexual cells. In phanerogams we find 

 undifferentiated cells in the buds. When the bud forms a 

 flower and sexual cells are developed in connection with it, 

 we learn that some of these undifferentiated cells are made 

 use of. It is entirely unknown to us how the transformation 

 of undifferentiated ceUs into sexual cells is caused. We can 

 observe with the microscope alterations in the structures of 

 the cells, but the cause of these alterations remains hidden 

 from us. In lower animals we find relations which to a 

 certain extent resemble those prevaihng in the phanerogams, 



