41 6 Louise Hoyt Gregory 



through conjugation. This is the only means of recovery from 

 deep depressions. Thus conjugation is a regulatory process to 

 bring about the normal relations between the nucleus and cyto- 

 plasm. Upon this theory, Hertwig has founded his theory of the 

 origin of sex cells and the determination of sex. Thus Hertwig 

 believes that an excess of nuclear material is the cause of the 

 periods of depression; that conjugation is the means of relieving 

 this depression, and that the conjugating cell is equivalent to a 

 depression cell. 



In a recent paper, PopofF ('07), a student of Hertwig, reaches 

 the following conclusions: 



A culture of Stylonychia, kept from April I to July 16, showed 

 periods of high vitality, which alternated with periods of low vital- 

 ity, or depression periods. These latter periods were accompa- 

 nied by a cessation of the ordinary life processes, also by morpho- 

 logical changes. 



These morphological changes included a great reduction of the 

 body size, from 360-320 to 90-200;^ and also a correspondingly 

 large increase in the size of the macro-nucleus. This change in 

 the size relations he considers the cause of the depression periods. 



As the depression periods became more and more serious, fewer 

 individuals were able to rally by a self-regulatory process, which 

 took place by a fragmentation of the nucleus, or by a direct expul- 

 sion of nuclear material into the cytoplasm. 



The tendency to conjugate is found only in deepest depression 

 periods, and is the means of restoration to normal conditions. 



PopofF has made his curve of the general vitality from daily 

 records of the division of ten individuals, and finds that in the 

 life history of three months and a half, five periods of depression 

 appear, the first and second a month apart and the last three two 

 weeks apart. Changes in food or temperature often cause fluctu- 

 ations in the daily records and a curve made from such records 

 is hardly as reliable as one made from the records averaged for a 

 longer period. If the curve of Stylonychia is plotted from average 

 records of five or ten day periods, it will be found to correspond 

 to the curves of Paramecium, Oxytricha and Tillina, each showing 

 the rhythmic periods of high and low vitality. (See Diagram V.) 



