550 H. S. Jennings and George T. Hargitt. 



conditions, between the volume of the nucleus and the volume of 

 cytoplasm; hence between the size of the nucleus and the size 

 of the cell. The amount of cytoplasmic material is readily regu- 

 lated so as to correspond with the volume of the nucleus. Hence 

 if at a given fission, as of Paramecium or Stentor, the nucleus 

 divides unequally, the cells taking origin at that time will likewise 

 be unequal. If now in future fissions both the cells divide as a 

 rule equally, we shall have two races permanently differentiated 

 in size. The explanation holds that in most fissions nuclear 

 divisions are equal, resulting in inheritance of a given typical 

 size in all the cells produced, but that occasionally, through acci- 

 dent or otherwise, an unequal nuclear division occurs, giving rise 

 to races of different size. The same thing is conceived to occur 

 in the formation of germ cells in Metazoa, the bodies formed of the 

 smaller cells being thus smaller — so that small races of both Met- 

 azoa and Protozoa arise in this way. 



Popoff first expounds this view on theoretical grounds, based 

 on general considerations following from Hertwig's theory of the 

 "Kernplasmarelation," taken in connection with the observed 

 existence of individuals of different size (Popoff, '08, p. 269, 

 274-275; 344-351). In a later paper ('09) he supports it by ob- 

 servations and experiments, coming finally to the conclusion that 

 "these results .... show clearly that the cell-size in a 

 Protozoan species is not something definite, but that it is extremely 

 variable, easily fixed at any desired grade of size, and transmis- 

 sible from generation to generation" (p. 148). There is a certain 

 amount of contrast between the condition that one would expect 

 to find if the cell size is "not something definite," but "extremely 

 variable," and the results of my study on precisely this point in 

 Paramecium, in my paper of 1908. In this study the cell size 

 was not found to be variable within a pure line, bat on the con- 

 trary showed a remarkable constancy, so that it was not possible 

 by long continued selection of large specimens or small specimens 

 from a given race to produce a race differing in size. These re- 

 sults of course do not show that change in size may not sometimes 

 occur in the manner set forth by Popoff. But the investigation in 

 Paramecium is felt to have been sufficiently extensive and thor- 



