382 STUDIES IN GENEKAL PHYSIOLOGY 



occurred at the same time as (or earlier than) in the eggs 

 from the same culture kept in oxygen. If the minimum 

 amount of oxygen necessary for cleavage is present, the 

 velocity of the cleavage is a function of the temperature and 

 not of the amount of oxygen present. It is important to 

 emphasize the fact that lack of oxygen at room temperature 

 does not retard cleavage, as does a reduction in the tempera- 

 ture. 



Finally, I convinced myself of the fact, through a special 

 series of experiments, that prolonged exposure to cold does 

 not diminish the power of the egg to divide. I allowed a 

 weak current of hydrogen to pass through a gas-chamber 

 which remained on ice for four hours. When I then exposed 

 the eggs to room temperature and continued to pass the 

 same weak current of gas through the chamber, all the eggs 

 divided. The majority reached the four-cell stage, and a 

 few even the eight-cell stage. Cleavage then ceased. If 

 not all the oxygen is driven -out, cleavage proportionate to 

 the amount of oxygen present still occurs in spite of the 

 prolonged cooling. We are, therefore, justified in conclud- 

 ing that when all the oxygen which it is possible to 'remove 

 from the Ctenolabrus egg is driven out, no complete cell- 

 division can occur. 



The question now arises in how far a division of the 

 nucleus is possible in such an egg. At the surface of the 

 Ctenolabrus egg a series of visible changes occurs before the 

 first cleavage. In the center of the nucleus several droplets 

 of a strongly refractive substance collect, which increase in 

 number and size, then coalesce, to resolve again into a large 

 number of minute droplets just before cell-division. These 

 droplets probably play a role, as we shall see later, in the 

 process of cell-division. It is possible, but not proved, that 

 their formation is a function of karyokinesis. These 

 changes in the strongly refractive substance also occur 



