LIFE HISTORY OF TWO RARE CILIATES 385 



hours of the growth period there was a rapid increase of proto- 

 plasm accompanied by a very slow growth of the nucleus, this 

 condition persisting up to within one hour and a half of the 

 next division, when the sudden and rapid growth of nuclear 

 material re-established the normal kernplasma-relation. 



Hertwig, in describing the relation of nucleus and plasma 

 in young cells says: "-Ich werde im folgenden diesen Zustand 

 der Kernplasma-Relation, mit welchem die Zelle in eine neue 

 Phase ihren Existenz eintritt, die Kernplasma-Norm nennen." 

 He designates by the term 'Kernplasma-Spannung" that period 

 in the life of the cell when the volume of the nucleus departs 

 from the Kernplasma-Norm. With a view to testing the valid- 

 ity of Hertwig's theory, careful measurements have recently 

 been made of nucleus and plasma in Tillina magna by Gregory 

 ('08); in sea-urchin larvae by Erdmann ('08); in Oenothera 

 lamarckiana and Oenothera gigas by Gates ('09j; and in Crepi- 

 dula and Fulgur by Conklin('ll). Gregory concludes: 



These facts seem to prove that there is no relation between the amount 

 of nuclear material in the cell and the general vitality of the proto- 

 plasm. In other words, the periods of weakness are not caused by 

 an excess of nuclear material. The nucleus may or may not increase 

 in size during periods of low activity; if an increase does take place, 

 it is generally found that the cytoplasmic material has increased also, 

 and the ratio between the two is the same as in periods of high activity. 



Erdmann studied the effect of temperature on the cell size, 

 finding the chromatin volume varied with the temperature and 

 concluding that the chromatin mass and not the number of 

 chromosomes was concerned, and that the cell-size was approxi- 

 mately proportional to this mass. Gates, on the other hand, 

 decided that the larger sized cells of Oenothera gigas result 

 from a doubling in the number of chromosomes and not merely 

 from an increase of chromotin mass. Gonklin, in summing 

 up the results of his observations on Crepidula and Fulgur says; 



In different eggs, corresponding blastomeres have approximately 

 the same kernplasma-relation; but in different blastomeres of the same 

 egg or of different eggs the kernplasma-relation is neither a constant 

 nor a self regulating ratio. It appears to be a result rather than a 

 cause of the rate of cell-division and consequently a variable rather 

 than a constant factor. 



