510 G. N. CALKINS AND L. H, GREGORY 



tion — was inhibited; metabolism weakened steadily until physi- 

 ological death carried off all of the race not artificially stimulated. 

 Finally, 'germinal death' preceded by the degeneration of the mi- 

 cronucleus and the cortical plasm, carried off the last individual. 

 These last individuals ''were of full size and were filled with gas- 

 tric vacuoles and partly digested food, while the body form was 

 normal" ('04, p. 446). It has since been shown that the micro- 

 nucleus is the center of divisional activity (Calkins '10), hence its 

 degeneration would account for the decrease in division rate and 

 the ultimate cessation of division 



In Woodruff's material on the other hand, the race is non-con- 

 jugating, hence no normal function has been suppressed by keep- 

 ing the individuals apart. So far as known the life history of 

 such non-conjugating forms has never before been undertaken 

 and Woodruff has shown that they will live for at least five and 

 one-half years. As Gregory pointed out these organisms can- 

 not be compared with those of the earlier experiments because of 

 essential differences in individual vigor. Conjugation further- 

 more has been prevented in one case and not in the other since 

 the power to conjugate is absent in the latter. Experimentation 

 has shown with some probability therefore, that we must dis- 

 tinguish between conjugating and non-conjugating lines of Para- 

 mecium in dealing with the questions of old age and natural 

 death. That these phenomena occur in the former has been 

 demonstrated for different types by Maupas, Jennings and Cal- 

 kins; that they do not occur in non-conjugating lines is still in 

 the experimenting stage. Five and a half j'-ears is indeed a long 

 period for Paramecium, but immortality is quite a different 

 matter. We conclude, therefore, that death from old age, by 

 which we mean the gradual weakening and final cessation of 

 vital activities, in Infusoria does occur in some forms but is not 

 yet demonstrated for others. 



