REPRODUCTION OF THE HYPOTRICHOUS INFUSORIA 51 



II. METHODS 



In order to study the life history of a number of the Protozoa, 

 Maupas isolated an individual in a favorable culture medium and 

 in the course of a few days, when a large number of animals had 

 arisen by fission, he counted the individuals, computed and re- 

 corded the number of divisions that had taken place, and isolated 

 one of the animals in another dish with fresh culture medium to 

 continue the culture. In some cases over 900 individuals were al- 

 lowed to accumulate before the isolation took place. Biitschli 

 later pointed out that there were two sources of error present in 

 such a method, namely, the difficulty of securing an accurate count 

 of so many organisms on a preparation at one time and the assump- 

 tion that the rate of division had been the same for all the animals 

 in the cultures, which might or might not be true depending en- 

 tirely upon the physiological condition of the different individu- 

 als of the culture. 



Calkins ('02) in his work with Paramaecium caudatum modified 

 Maupas method in order to overcome these difficulties. Instead 

 of using a large receptacle and allowing the animals to accumulate 

 in large numbers before isolation, he kept them on glass slides 

 having a central depression holding about five drops of the culture 

 medium, and from these slides he isolated an individual every one 

 or two days so that only a few were present at the time of isolation. 

 This method of isolation, besides giving the exact number of gener- 

 ations through which the culture has passed, also prevents con- 

 jugation occurring in the slides of the main lines which are isolated 

 daily. This method very little modified has since been used by a 

 number of investigators, and notably by Woodruff in his work 

 with Paramaecium aurelia. The cultures discussed in this paper 

 have all been conducted by this same method and as it has noAV 

 become well-known only a brief description of the process will be 

 given. 



The animals to be studied were isolated on glass slides having a 

 central depression large enough to hold five drops of water. The 

 slides to prevent evaporation were kept in moist chambers made 

 from large Stender dishes with ground glass covers, and each hav- 

 ing a capacity of eight slides. In starting a culture, an animal was 



