Sex as an Adaptation 443 



The individuals in question, in which this interchange of 

 micronuclei has taken place, undergo a change, and behave 

 differently from what they did before. They feed, become 

 larger and less vacuolated, and are more active. They soon 

 begin once more to divide. Maupas found that an individual 

 that has conjugated will run through a new cycle of divisions, 

 which will, however, after a time also slow down, unless con- 

 jugation with another individual having a different history 

 takes place. If conjugation is prevented, the individual will 

 die after a time. These results seemed to show that the 

 division phase of the life history cannot go on indefinitely, 

 and that through conjugation the individual is again brought 

 back to the starting-point. 



Quite recently Calkins has carried out a somewhat similar 

 series of experiments, which have an important bearing on 

 the interpretation of Maupas' results. The experiment of 

 isolating an individual and tracing the career of its descen- 

 dants was repeated with the following results : two series 

 were started, the original forms coming from different locali- 

 ties. Of their eight descendants four of each were isolated. 

 The remaining four of each set were kept together as stock 

 material. The rate of division was taken as the measure of 

 vitality. The animals divided more or less regularly from 

 February to July. After each division (or sometimes after 

 two divisions) the individuals were separated. About the 

 30th of July the paramcecia began to die " at an alarming 

 rate, indicating that a period of depression had apparently 

 set in, or degeneration in Maupas' sense." Up to this time 

 the animals had been living in hay infusion, renewed every 

 few days, from which they obtained the bacteria on which 

 they feed. Calkins tried the effect of putting the weakened 

 paramcecia into a new environment. Infusion of vegetables 

 gave no good results, but meat infusions proved successful. 

 " The first experiment with the latter was with teased liver, 

 which was added to the usual hay infusion. The result was 



