30 ARTIFICIAL PARTHENOGENESIS 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 fertilized eg¢ 
remains unaltered during lack of oxygen or presence of potas- 
sum 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 ne 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 e.c. 1/20 per cent 
KCN solution.? At different intervals, samples of these eggs 
1Loeb, Archiv f. 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. 
