REPKODITCTION OF THE HYPOTRICHOUS INFUSORIA 225 



the death of the Ph culture, and in figure 11 is shown another 

 normal individual from the same culture preserved October 20, 

 1913, about IS months after the death of the Ph cutture and 6 

 months after the death of the Pb culture. As has been noted above, 

 no ab7iormal specimens have ever been found in the Phtt culture 

 during its entire history, covering, thus far, a period of over 22 

 months. 



V. DISCUSSION AND CONCLUSIONS 



A number of investigators have noted the fact, as shown in 

 these experiments, that closely related species of the Infusoria, 

 or even different races of the same species, vary greatly in regard 

 to culture conditions that are adapted to them. Jennings and 

 Hargitt ('10), working on a number of different races of para- 

 maecia, found that culture conditions which were apparently ideal 

 for a certain race of Paramaecium might not be at all suitable for 

 another race. Woodruff ('11) found that culture conditions which 

 were entirely suitable for his Paramaecium aurelia cultures and 

 on which they had thrived for years were not entirely adapted 

 for a race of Paramaecium caudatum. The experiments of 

 Woodruff ('12), in his researches on the protozoan fauna of hay 

 infusions, indicate that the animals are adapted for only certain 

 conditions of the medium, and when these conditions are at- 

 tained, they are present in maximum numbers, and as the con- 

 ditions in the infusion change they disappear and other forms 

 become dominant which are adapted to the new conditions. 



In Part I of these studies, the writer ('12) was able to show 

 that it is possible to change greatly the life history of Stylonichia 

 pustulata by employing dilTerent kinds of culture media. In a 

 culture bred on beef extract medium conjugation occurred, where- 

 as, in another culture of descendants from the same original 

 animal but kept on a hay infusion medium, conjugation did not 

 occur at any time. The animals in the beef culture died at the 

 403d generation while those on the hay medium attained 572 

 generations. The experiment was repeated by starting another 

 culture on the beef extract medium with animals from the hay 

 culture after the first beef culture had died, and again conjuga- 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 2 



