2 LORANDE LOSS WOODRUFF 



at division stages of Spirogyra, are both retained in one of the 

 daughter cells, that cell becomes unusually large. Boveri ('02, 

 '05) found that the size of the .nuclei of the cells of sea urchin 

 larvae is directly proportional to the number of chromosomes 

 which enter them, and that cells which contain small nuclei are 

 below the normal size, because such cells divide more frequently 

 than those with large nuclei. 



In a number of publications, the earliest of which appeared 

 in 1890, Minot advanced the view that differentiation, senescence 

 and death are concomitant with, and the result of, an increase in 

 the proportion of cytoplasm to nucleus in cells. 



Minot holds that the egg, at the earliest stage of its develop- 

 ment, is actually in a senile state in which there is an excessive 

 amount of cytoplasm as compared with the nucleus. During the 

 process of cleavage, however, this relation is reversed by a rapid 

 increase in the nuclear material. Thus rejuvenation is brought 

 about chiefly by the segmentation of the egg, and depends upon 

 the increase of the nucleus; and senescence gradually appears as 

 development proceeds on account of the increase of the cytoplasm 

 which is necessary for the differentiation of the cells. He wrote 

 ('97, p. 3705 : 



The animal, when it is young, has cells with a small amount of pro- 

 toplasm In order that perfection of the adult structure 



should be attained, it is necessary that the mere undifferentiated cells, 

 each with a small body of protoplasm, should acquire first an increased 

 amount of protoplasm, and then from the increased protoplasm should 

 be taken the material to result in differentiation, in specialization. 

 The increase of the protoplasm is ... . the mark 

 both of advancing organization and advancing age. 



In regard to the lower forms Minot says: 



If it be true that there is among Protozoa, among unicellular animals, 

 anything comparable to the gradual decline in the growth power which 

 occurs in us we shall expect it to be revealed in the condition of the 

 cells — -to see in those cells which are old an increase in the proportion 

 of protoplasm, and consequently a diminution in the relative amount 

 of nucleus (p. 515). 



« 



The interest in the relative amount of nuclear to cytoplasmic 



materials in cells has been largely augmented by the contributions 



