THE RELATION OF RHYTHMS AND ENDOMIXIS, 



THEIR PERIODICITY AND SYNCHRONISM 



IN PARAMECIUM AURELIA. 



R. T. YOUNG, 

 UNIVERSITY OF NORTH DAKOTA. 



Periodic nuclear reorganization or endomixis in Paramecium, 

 noted by Hertwig ('88-89) an d since then by many other in- 

 vestigators, and described in detail by Woodruff and Erdmann 

 ('14), is of great interest because of its bearing on questions of 

 parthenogenesis, immortality and nuclear functions in Protozoa 

 primarily, and secondarily in organisms in general. In a series 

 of recent papers Woodruff and Erdmann ('14, '16) and Woodruff 

 ('17, a and &) have advocated the view that it is a sine qua non 

 in the life of Paramecium, that it is a rejuvenating process 

 analogous to the similar process in conjugation, and that it 

 usually occurs at the low point in the division rate between two 

 "rhythms," the time interval of which is a fixed quantity in- 

 herent in the species and which cannot be modified by the ex- 

 ternal environment. 



Kasanzeff ('01), Popoff ('09), Sun ('12) and myself (Young, 

 '17) have shown that external agents may serve to induce en- 

 domixis, and my own experiments show that the frequency of its 

 occurrence may be increased in this way. In my paper (/. c., p. 

 52) I have stated that " It is more or less cyclical in character and 

 probably has a rejuvenating function. It is not however a 

 necessary accompaniment of temporary depressions and may 

 not be followed by rejuvenation." I have pointed out several 

 cases of the occurrence of low division points without endomixis 

 in Woodruff's and Erdmann's experiments, as well as in my own. 

 I have also indicated one case in their experiments and one in my 

 own in which the process was associated with a rising, rather than 

 a falling division rate; and have shown that in some instances 

 endomixis is not followed by rejuvenation. 



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