150 Life and Death, Heredity and Evolution 



cence as a general result of mating. Indeed it is only fair to 

 say that most of the positive evidence is against rejuvenes- 

 cence of any sort. In Paramecium, not only do those that 

 have conjugated multiply less rapidly than before, but a 

 great many of them die after conjugation, although with- 

 out conjugation they live vigorously. Many others are weak 

 and sickly, multiplying but little. Still further, conjugation 

 produces a great number of abnormalities and monstrosities, 

 such as do not occur without mating (see Figure 44). In 

 many other infusoria all or nearly all those that have con- 

 jugated die, or completely cease multiplying. Maupas made 

 many investigations giving such results. He allowed two 

 unrelated cultures of Stylonychia to become degenerated, 

 then let them conjugate together; according to the theory 

 this ought to have rejuvenated them. But it did not; they 

 all died. He found that even in wild Stylonychias conjuga- 

 tion rather usually results in death ; later students have con- 

 firmed this. In his experiments, Maupas found that the 

 individuals that have conjugated all die in Spirostomum, 

 Climacostomum and Didinium. In Leucophrys he found 

 that a large proportion of those that mate die. It used to 

 be supposed that such results were due to the fact that the 

 animals had become so degenerate that even conjugation 

 could no longer save them. But we now know that under 

 proper conditions, without conjugation they would (in most 

 cases at least) live and multiply vigorously, while after con- 

 jugation they are weak or die. 



Such facts are most extraordinary; they are difficult to 

 explain on any theory. A priori it appears that the re- 

 placement of the old active nucleus by the reserve nucleus, 

 must tend to give rejuvenescence in conjugation, just as 

 when it occurs without conjugation. But this tendency is in 

 the majority of cases completely overwhelmed and done away 

 with by other features of mating; by the physiological diffi- 



