48 GEORGE ALFRED BAITSELL 



not occur before the 170th generation senile degeneration set in, 

 resulting in an abnormal diminution in size of the organisms and 

 other pathological conditions and culminating in a complete dis- 

 appearance of the micronuclei. This senile degeneration reached 

 its climax at the 316th generation at which point all the non-con- 

 jugants would die. This author also held that conjugation in 

 order to be fertile- must occur between gametes of diverse ances- 

 try, and that the phenomenon would not take place except when 

 the animals were in a medium in which there was a scarcity of 

 food. 



Maupas believed that these requirements were necessary for 

 fertile syzygies not only in S. pustulata but also, with some differ- 

 ences in time of sexual maturity, for all Infusoria and that senile 

 degeneration would always occur provided conjugation did not 

 take place during the so-called period of maturity. He upheld 

 then the view that rejuvenation by means of conjugation was nec- 

 essary for the continued existence of the organisms. In case it 

 did not occur the life cycle would end after a fairly definite number 

 of generations. 



Joukowsky ('98) found, as had been previously announced by 

 Biitschli ('76), that in Paramaecium putrinum fertile syzygies 

 could occur between individuals only a .very few generations re- 

 moved from conjugation. In a number of instances only seven or 

 eight generations elapsed before fertile unions occurred between 

 descendants of a single isolated ex-conjugant. This investigator 

 also kept Pleurotricha through 458 generations in eight months 

 without the occurrence of either conjugation or degeneration. 



Calkins ('02a) in his study of the life history of Paramaecium 

 caudatum found that fertile syzygies occurred at the 350th, 410th, 

 467th and 500th generations, thus showing that, in this form at 

 least, the so called period of sexual maturity really has no signifi- 

 cance. He also showed that conjugation between closely related 

 gametes was as generally fertile as in the cases where the gametes 

 were of diverse ancestry. Scarcity of food was shown to be not a 

 sufficient factor to induce conjugation and finally, while some evi- 

 dences of degeneration were noted in the animals of the cultures 

 at times, such as low division rate, dimished size, and occurrence 



