414 Louise Hoyt Gregory 



vented but the vegetative elements again become active, and a com- 

 paratively high division rate follows, though not for a continued 

 period. Paramecium aurelia shows a still higher degree of sen- 

 sitiveness of the protoplasm. As a result of treatment with salts, 

 the protoplasm renewed its activities, a high division rate followed, 

 and this condition continued through a period of six months. 

 Such a marked response to stimulation brings us close to the facts 

 of artificial parthenogenesis. The unfertilized egg may be con- 

 sidered to be in a state of physiological depression, its vegetative 

 activities are undeveloped and unless some stimulus is given, it \\ill 

 die. ^Experiments have shown that through treatment with salts, 

 the egg renews its activities, divides, and development follows as 

 if normal fertilization had taken place. Thus, if an unfertilized 

 egg is stimulated artificially to develop, the term artificial partheno- 

 genesis is applied. If a protozoan is artificially stimulated to 

 renew its weakened activities, the term artificial rejuvenation is 

 used. Both terms apply to different degrees of the same pro- 

 toplasmic reaction, and are relative only. Artificial rejuvenation 

 must be applied to the condition found in Tillina as well as to 

 those of Oxytricha and Paramecium. The term cycle, likewise, 

 is relative only. If we can speak of but one in the life history so 

 far known in Tillina, why should we speak of more than one in 

 the history of Paramecium or Oxytricha where the difference in 

 the vitality of the protoplasm is one of degree only .^ Enough 

 consideration has not been taken of the fact that not only does each 

 individual vary in its degree of sensitiveness at different periods 

 in the life history, suggested by Towle, and shown by the rhythms 

 of Woodruff, but each individual of the same species as well as 

 of different species has its own peculiar protoplasmic reactions. 

 Woodruff himself, has failed to consider this fact in his last paper 

 on the effects of a varied environment on Paramecium. He has 

 carried a culture 'of Paramecium for a year on a medium that has 

 been constantly changed, and so far he finds no indication of any 

 marked periods of weakness such as Calkins found appearing at 

 fairly regular intervals in those forms kept on a constant hay infu- 

 sion diet. From this Woodruff concludes that the unchang^ed 

 diet was abnormal, and caused the periods of low vitality which 



