NUCLEOPLASMIC RELATIONS IN ARCELLA 79 



and Dileptus is particularly striking. Not only was the K/P 

 ratio large when the organisms were subjected to a low tem- 

 perature, but when a higher temperature was subsequently 

 substituted conjugation took place involving a reorganization 

 of the nuclei and the acquisition of the normal K/P ratio for 

 the higher temperature. 



Other external factors that appear to affect the nucleocyto- 

 plasmic ratio are overfeeding and starvation. Hertwig caused 

 an increased K / P ratio in Actinosphaerium and certain Infusoria 

 by overfeeding, and Kasanzeff ('01) obtained a similar result 

 in Paramecium by starving the organisms. 



Many investigators have studied the nucleocytoplasmic 

 relations in Protozoa and in Metazoa, confirming in part the 

 conclusions reached by Hertwig and his followers. The work 

 of Minot ('08), however, leads to a theory directly opposed 

 to that of Hertwig. Minot finds that in segmenting eggs the 

 amount of nuclear material increases as compared with the 

 quantity of cytoplasm, and concludes that this increase is indica- 

 tive of the process of rejuvenescence. Rejuvenescence is thus 

 revealed as an increase of the nuclear material, and senescence 

 as an increase and differentiation of the cytoplasm. When 

 applied to Protozoa, Minot's theory requires ''in those cells 

 which are old an increase in the proportion and in the differen- 

 tiation of the protoplasm [cytoplasm], and consequently a dimi- 

 nution in the relative amount of nucleus" ('08, p. 231). 



Conklin ('12) disagrees with both Hertwig and Minot regard- 

 ing the connection of the nucleocytoplasmic relation with 

 senescence and rejuvenescence, but accounts for these phe- 

 nomena by decreases and increases in metabolism. His studies 

 of Crepidula show that great variation exists in the nucleo- 

 cytoplasmic relations of different blastomeres, but that the 

 ratio between nucleus and cytoplasm is similar in corresponding 

 blastomeres of different eggs. He does not believe that cell 

 division in Crepidula is initiated by limitations of the working 

 sphere of the nucleus nor by a nucleocytoplasmic tension; but 

 is related to the rate and nature of the metabolism in the cell. 

 Somewhat similar conclusions were reached by Woodruff ('13) 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY. VOL. 30, NO. 1 



