8 HEREDITY AND SEX 



Maupas found by following from generation to 

 generation the division of some of these protozoa that 

 the division rate slowly declines and finally comes to 

 an end. He found that if a debilitated individual 

 conjugates with a wild individual, the death of the race 

 is prevented, but Maupas did not claim that through 

 conjugation the division rate was restored. On the 

 contrary he found it is lower for a time. 



He also discovered that conjugation between two 

 related individuals of these weakened strains produced 

 no beneficial results. 



Biitschli had earlier (1876) suggested that conjugation 

 means rejuvenation or renewal of youth, and Maupas' 

 results have sometimes been cited as supporting this 

 view. Later work has thrown many doubts on this 

 interpretation and has raised a number of new issues. 



In the first place, the question arose whether the 

 decline that Maupas observed in the rate of division 

 may not have been due to the uniform conditions under 

 which his cultures were maintained, or to an insuflfi- 

 ciency in some ingredient of these cultures rather than 

 to lack of conjugation. Probably this is true, for 

 Calkins has shown that by putting a declining race 

 into a different medium the original division rate may 

 be restored. Woodruff has used as culture media a 

 great variety of food stuffs and has succeeded in keep- 

 ing his lines without loss of vigor through 3000 gen- 

 erations. Maupas records a decline in other related 

 protozoa at the end of a few hundred generations. 



Biitschli's idea that by the temporary union (with 

 interchange of micronuclei) of two weak individuals 

 two vigorous individuals could be produced seems 



