3O4 L. L. WOODRUFF. 



tial of division and those which are most readily acclimated to 

 changes in their medium. Each and all of these factors may 

 contribute to the length of the life of the culture but after all 

 is done the " chances " are largely against the prolonged life of 

 the culture. 



This culture suggests, then, the time-honored question whether 

 the protoplasm of infusoria has the potential of unlimited life 

 and reproduction, and the fundamental question as to the role 

 of conjugation in the life history of these organisms. Up to the 

 present time there has been no tendency to conjugate among the 

 individuals of this culture, although in the " stock " cultures, 

 consisting of the individuals remaining over after the daily isola- 

 tions, there has been ample opportunity for it to take place. The 

 daily isolations, of course, have precluded its occurrence in the 

 four direct lines of the culture. This result agrees with those of 

 Joukowsky on 3460 generation culture of Plenrotriclia lanceolata, 

 Gregory on a 548 generation culture of Tillina magna, and 

 Woodruff on an 860 generation culture of Oxytricha fallax, on a 

 448 generation culture of Pleurotricha lanceolata and on a 288 gen- 

 eration culture of Gastrostyla steinii. Maupas secured no conju- 

 gations in his cultures of Stylonychia mytilus and Oxytricha sp., 

 though his other series yielded plenty of syzygies. That the 

 infusoria do conjugate is, of course, a matter of common observa- 

 tion ; but I believe these results indicate that the phenomenon is 

 not so frequent in the life history as is generally believed. A 

 daily examination of twenty hay infusions, made up by several 

 different methods, has not shown a single case of conjugation 

 among the hypotrichous forms present either at the top or bottom 

 of the jars. In fact, not a single syzygy has been observed in 

 any species except Parameciiim, and in this form conjugation has 

 been very rare. However, a sudden transference of the para- 

 mecia from the comparatively constant culture medium of a hay 

 infusion to a different medium has produced marked epidemics 

 of conjugation. It is just possible that a constant medium is 

 necessary for the so-called miscible state (Calkins) to develop, 

 and that this becomes functional on transference to a decidedly 

 different medium. If this is so, it may account for the absence 

 of conjugation in my paramecia series on a varied medium, and 



