B80 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 
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