NUCLEO-CYTOPLASMIC RELATION OF OXYTRICHA 21 



of nucleus to cytoplasm in Stylonychia, while the increase of 

 both cytoplasm and nucleus in Oxytricha resulted (as we have 

 seen) in a decrease in the proportion of nucleus to cytoplasm, 

 owing to the slightly smaller increment of the nucleus as 

 'compared with that of the cytoplasm. 



It cannot be doubted that the relative volume of cytoplasm 

 and nucleus plays an important part in the life of every cell 

 and that inconceivably small variations may, and probably do, 

 produce far reaching disturbances many of which are not detect- 

 able. Likewise, I believe, it is a priori beyond the limits of prob- 

 ability that significant morphological changes would be as a 

 rule of such a magnitude as to be measurable. Undoubtedly 

 a morphological basis should be sought for the various physiolog- 

 ical manifestations in degenerating cells, but, I believe, that the 

 results so far at hand indicate that it is prejudging the problem 

 and attempting to reduce it to unduly simple terms, when mere 

 measurable mass relations are estimated as fundamental criteria. 



My results with various cultures of Protozoa lead me to 

 agree with the view that senescence seems to be associated 

 with decreased metabolism and rejuvenescence with increased 

 metabolism, but I am unable to correlate with these physiological 

 factors any constant morphological changes such as the current 

 nucleo-cytoplasmic relation theories demand. 



VII. SUMMARY 



1. A wide variation in the size of the cells and of the nuclei 

 occurs at all periods of the life of the race. 



2. The mean size of the cell is smallest at periods of high repro- 

 ductive activitity and becomes progressively larger as the division 

 rate falls. 



3. The mean size of the nucleus is smallest at periods of high 

 reproductive activity and becomes progressively larger as the 

 division rate falls. 



4. The nucleo-cytoplasmic relation of individual cells shows 

 a wide variation at all periods of the life of the race. 



5. The mean proportion of nuclear to cytoplasmic material is 

 highest during the period of greatest reproductive activity. 



