The Intimate Causes of Old Age. 219 



even as the multicells. The Weissmann hypothesis asso- 

 ciaited death with sexual reproduction in the multicells, 

 and portrar^d the causes of death as oiganic and extra- 

 cellular. We nowJearned that the causes of death are 

 intracellular. Colonies oT "unicells congregate to be re- 

 generated by blending and exchange of ~paiiicles, sexually, 

 not differently in principle from the sexual congress of 

 animals. Unicells increase in number by division of the 

 adult, parturient cell into two smaller " daughter cells," 

 each of which grows and divides into two others, genera- 

 tion on generation, for a limited length of time, but not 

 indefinitely, as was at one time believed to be true of 

 them. 



On the contrary, after a certain number of cell genera- 

 tions such unicells must get together sexually. The 

 millions of rhizopods in a stagnant pool, for example, 

 must thus congregate or they will cease to be reproductive 

 and the species will die of old age. 



As observed by Maupas in 1885-86, and other observers 

 since, sexual conjugation is accompanied by profound 

 changes in the cells. The technique of these changes is 

 of less consequence here than an appreciation of the 

 principle involved. When two of the conjugating cells 

 have paired and come into close contact, the paranucleus, 

 or sex organ, of each suffers a species of dissolution ; it 

 divides and appears to undergo a kind of reorganization ; 

 certain parts of it are rejected altogether and cast forth. 



