30 Artificial Pabthenogenesis and Fertilization 



According to Conklin, the average nuclear growth during cleav- 

 age is not more than 5 per cent to 9 per cent for each division up 

 to the thirty-two-cell stage. The possibility remains that the 

 slight increase in the rate of oxidations with progressive cell 

 divisions is due to the increase of the mass of the nuclei. This 

 would be intelligible on the assumption that the rate of oxida- 

 tion is in proportion to the mass of the nuclei. Such a view 

 would harmonize with the suggestion expressed formerly by the 

 writer, that the nucleus might be the main (although not the 

 only) oxidizing organ of the cell.' 



4. The observation that the nucleus of the fertihzed egg 

 remains unaltered during lack of oxygen or presence of potas- 

 s'um cyanide shows that oxidations are the prerequisites of the 

 mechanical processes of nuclear and cell division. It can, 

 however, be shown that aside from oxidations other chemical 

 processes are accelerated in the sea-urchin egg by the process of 

 fertilization. When fertilized eggs of Strongylocentrotus pur- 

 puratus are left in sea-water free from oxygen for twenty- 

 four hours at 15° C, they will not develop during that time, 

 but they will begin to develop at once if oxygen is admitted. It 

 will be found, however, that their development is no longer 

 normal, since they form abnormal blastulae and never or rarely 

 reach the gastrula stage. If unfertilized eggs are kept for 

 twenty-four hours without oxygen they remain perfectly normal, 

 since upon addition of sperm they develop normally and reach 

 the pluteus stage. The result is the same if instead of with- 

 drawing the oxygen we retard the oxidations by the addition 

 of KCN. 



Unfertilized and fertilized eggs of the same female were 

 placed in a bowl with 50 c.c. of sea-water -|-2 c.c. 1/20 per cent 

 KCN solution.2 At different intervals, samples of these eggs 



1 Loeb, Archiv /. Entwicklungsmechanik, VIII, 689, 1899. Some authors 

 attribute to me the opinion that in the protoplasm no oxidations occur. I have 

 never expressed such an opinion. 



2 Such a solution stops the segmentation in fertilized eggs. 



