RELATIVE SENSITIVENESS OF FISH EMBRYOS 311 



second smaller one containing the eggs and a little sea-water 

 (about 2 to 3 c.c.). The out6r 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 as a 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 



