VITALITY 



251 



The above method was first used in connection with the life 

 history of Paramecium caudatum (Calkins, 1904), and many other 

 experiments of similar nature were made on this genus by later 



1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 l'J 20 21 222324 25 26 27 28 2<> 30 31 323334 3536 37383940 41 



Fig. 131. — Composite graph of vitality of twenty-three series of Uroleptus mobilis, 

 each having vitality of more than 85 per rent (solid line). The ordinates represent 

 the average numbers of divisions in ten-day periods. The dotted line is the vitality 

 graph of the double organism. (After Calkins.) 



observers. It turned out to be an unfavorable subject in some 

 respects for the study of this particular problem of vitality, for in 

 1914 Woodruff and Erdmann announced the discovery of a periodic 



Fig. 132. — Vitality graph of Pleurotricha lanceolata. (After Baitsell.) 



reorganization process without conjugation or encystment in Para- 

 mecium aurelia which is exactly comparable with one type of 

 parthenogenesis occurring in Metazoa (see p. 316). The discovery 



