RELATIVE SENSITIVENESS OF FisuH EmsBryos 3811 
second smaller one containing the eggs and a little sea-water 
(about 2 to 3.c.c.). The outer test-tube is then sealed. By 
putting splinters of glass into the bottom of the outer test- 
tube the smaller test-tube is kept above the surface of the 
pyrogallol. This arrangement allows one to observe the 
eggs, and at the same time to shake the apparatus in order 
to accelerate the absorption of oxygen. In some of the 
experiments the sea-water in which the eggs were con- 
tained was boiled, in others this was not done. The result 
was, however, not very different in the two cases. Lack of 
proper laboratory facilities did not allow me, however, to 
study how rapidly and how completely the oxygen is absorbed 
by the pyrogallol in these experiments. But even if the 
absorption of oxygen was not complete in these experiments, 
it was nevertheless equally incomplete in all the experiments. 
Since we are interested in our experiments only in the relative 
sensitiveness to lack of oxygen, a quantitative determination 
of the oxygen absorbed was not absolutely necessary, if the 
lack of oxygen was only always the same. For the sake of 
brevity, I will designate the apparatus used for the absorp- 
tion of oxygen as an “oxygen vacuum.” The temperature 
was usually 22-24° C. Fundulus eggs require a relatively 
high temperature for their development. 
2. Some eggs of Fundulus were introduced, one-half 
hour after (artificial) fertilization, into a large number of 
test-tubes from which the oxygen was absorbed by the 
method given above. One of these sealed test-tubes was 
opened at different intervals, and the eggs were compared 
with eggs from the same culture which had remained in 
normal sea-water asa control. It was found that cleavage 
occurred in the oxygen vacuum, and at first even a little more 
rapidly than in normal sea-water. The latter was, however, 
probably only the result of the rise in temperature brought 
about in melting the glass for the purpose of sealing the 
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