NUCLEO-CYTOPLASMIC RELATION OF OXYTRICHA 11 



which comprise about seven hundred specimens. It is unportant 

 to emphasize the fact that in the present study are considered 

 specimens only from periods in which the regular culture medium 

 was employed, and also those only from the direct lines of the 

 culture. The specimens preserved from the stock cultures (i.e., 

 mass cultures seeded from the main lines) have been omi^^ted. 

 This left over 450 specimens of the pedigreed race for measure- 

 ment. These specimens cover nearly the entire range of the life 

 of the race, but of necessity a majority are representatives of 

 periods of comparatively high division rate (fig 1, B and C). 

 The methods necessary for the breeding of pedigreed cultures 

 make it impossible to kill and preserve a large number of speci- 

 mens when the rate is low, because at such periods it is essential 

 to keep alive all annuals available to ensure the continuance of 

 the strain. It is believed, however, that whatever may be lost 

 in accuracy, by not having larger numbers to measure at certain 

 depression periods, is far more than counterbalanced by the fact 

 that the ancestry and the environmental conditions of those 

 studied is accurately known. 



It was apparent when the material was surveyed that it was 

 impossible to secure measurements which would give accurately 

 the volume of either cytoplasm or nucleus during the periods of 

 marked physiological depression owing to the irregular contours 

 of the cells and particularly of the nuclei. Accordingly, it was 

 determined first to make accurate measurements of the areas of 

 the cells and their nuclei throughout the entire life of the race — 

 as only by this method could the size of the cell and nucleus 

 dm'ing marked depression periods (A, D) be compared with 

 those during periods of comparatively high reproductive activity 

 {B, C). 



Since from these data it was impossible to determine the rel- 

 ative volu*me of cytoplasm and nucleus at the different periods 

 of the hfe history, it was decided to investigate this point with 

 respect to the specimens from periods B and C, during which the 

 rates of division were characteristically different, while the form 

 of the cells and their nuclei was sufficiently regular to permit 

 the computation of their volumes from linear measurements. 



