382 STUDIES IN GENERAL PHYSIOLOGY 



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

 from the same culture kept in oxygen. If the minimum 

 a HIGH nt of oxygen necessary for cleavage is present, lite 

 rclocity of the cleavage is ((function of the temperature and 

 not of the amount of o-i'i/<jen 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 

 ircak 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 /// s/tifc of f//c 

 prolonged cool in;/. We arc, therefore, justified in coin-lad- 

 ing that irlicn all ///c (u-i/i/cn irlu'rh it is possible to remove 

 from the Cfenoldlirns <></</ is drircn out, no complete ccll- 

 dirision 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 



