380 STUDIES IN GENERAL PHYSIOLOGY 



Must we now assume that Ctenolabrus is able to divide 

 two or three times without oxygen? The first cleavage of 

 the Ctenolabrus egg occurs in from fifty to seventy minutes 

 after fertilization, according to temperature; the second, 

 about fifteen to thirty minutes later. It is entirely possible 

 that even in a strong current of hydrogen all of the oxygen 

 is not driven out of the eggs in so short a time. In order 

 to settle this point, I made a long series of experiments in 

 the manner described above, in that I introduced the eggs 

 immediately after fertilization into two gas chambers, one of 

 which was kept on ice, while the other was exposed to room 

 temperature, and passed the same stream of hydrogen 

 through both. I will describe a few of these experiments 

 here. In order to be brief, I will call the eggs upon the ice 

 the experimental eggs, the .others the control eggs. 



In one experiment the control eggs divided into two cells 

 fifty minutes after fertilization, when the experimental eggs 

 were removed from the ice, while the stream of hydrogen 

 was kept up uninterruptedly. In thirty minutes the first 

 cleavage occurred in the experimental eggs. At the same 

 time the control eggs went into the four-cell stage, and 

 twenty-five minutes later the experimental eggs also went 

 into the four-cell stage. Cleavage then ceased in both 

 chambers. Even though hydrogen had been conducted 

 through the chamber containing the experimental eggs, 

 which had been kept on the ice for a long time before 

 the beginning of cleavage, and the oxygen had probably 

 been driven out more thoroughly than in the control eggs, 

 cleavage nevertheless occurred in the same way in both. 

 There was only one difference ; all the control eggs reached 

 the four-cell stage, while about 25 per cent, of the ex- 

 perimental eggs remained in the two-cell stage. 



In another experiment the experimental eggs remained 

 for one hour and forty minutes on the ice. During the first 



