22 Life and Death, Heredity and Evolution 



in the prevalent views, I believe that the last few years have 

 brought us the facts which answer these questions. It is 

 of these that I wish first to speak; they form a foundation 

 for all our knowledge of these matters in Protozoa. 



Although it appears that these creatures do not naturally 

 die, it is equally apparent that they do reproduce. Every 

 day or two, or even more frequently, each individual divides, 

 and we have two where there was but one; in a few days 

 their number has multiplied enormously. And if we watch 

 them long and closely enough, we make another discovery 

 of great interest: after the passage of many generations 

 these creatures mate, as do higher animals and plants. Two 

 individuals unite and exchange parts of their bodies (figure 

 6), then separate and both continue to live and to reproduce 

 as before. 



Figure 6. Conjugation of Paramecium. 



Now if these creatures do not die, why should they mate 

 and why should they reproduce? In ourselves and in the 

 animals we know intimately, mating and reproduction are 

 the prelude to death; reproduction seems a method of re- 

 placing the individuals that are to die. What is the use 

 of these processes if those now alive are to continue to 



