366 



THE AMERICAN NATURALIST 



[Vol. XLVI 



NUCLEAR GROWTH DURING EARLY DEVELOPMENT 



In reading Conklin's recent paper on the relative growth of 

 nucleus and cytoplasm in developing eggs, 1 I was at first some- 

 what puzzled by certain of the relations brought out. The mat- 

 ter is one that bears directly upon so many important problems, 

 and Conklin's paper is one of such fundamental importance, 

 that possibly a statement of the difficulty and its apparent solu- 

 tion may be worth while. Work done with the thoroughness 

 that characterizes all that Conklin puts forth partakes to a cer- 

 tain degree of the inexhaustibleness of nature, in that it is pos- 

 sible to discover in it relations not explicitly set forth by the 

 author. 



Conklin's most notable result is that the relative proportions 

 of nuclear and cytoplasmic materials do not appreciably change 

 during early development, as they have been supposed to do. 

 The bearing of this upon the theory that cleavage is a prcfcess of 

 rejuvenescence, owing to the enormous increase of nuclear ma- 

 terial relative to the cytoplasm, is evident. The point which I 

 wish to discuss has no bearing upon this fundamental result, but 

 relates to the rate of nuclear growth. 



On this point Conklin sums up his results for Crepidula as 

 follows : 



"The rate and amount of nuclear growth during cleavage is much 

 less than is generally believed. Whether the nuclear volume is taken 

 when the nuclei are at their maximum, mean or minimum size, the 

 nuclear growth is far from 100 per cent, or a doubling, in each division. 

 In Crepidula the nuclear growth is not more than 5 per cent, to 9 per 

 •cent, for each division from the 2-cell to the 32-cell stage, and less than 

 1 per cent, for each division after the 32-cell stage" (p. 40). 



Similar figures are given for the other animals studied. 



Now, if I have gotten clear on the matter, what Conklin here 

 means is that when any cell divides, the increase of nuclear ma- 

 terial thus produced is on the average but 5 to 9 per cent, of the 

 amount that ivas present in an early stage of the egg, and spe- 

 cifically in the two-cell stage. This is a different method of ex- 

 pressing the rate of growth from that often employed. The 

 question perhaps most often answered when the rate of nuclear 

 growth at cell division is given is the following: How much is 

 Conklin, E. G., "Cell Size and Nuclear Size," Journal of Experimental 



