PHYSIOLOGICAL EFFErots or Lack oF OxyGen 399 
previous papers that such eggs do not lose their power of 
dividing even after being kept for three to four days with- 
out oxygen. On the other hand, I noticed a collection of 
the strongly refractive droplets in the furrows between the 
cells in Fundulus eggs also. Our observations on the 
mechanics of cell-division, therefore, seem to hold also for 
the Fundulus egg, only that the material for the surface 
layer of the Fundulus cells seems to be different chemically 
from that of the Ctenolabrus cells in that the latter in the 
lack of oxygen flows together into droplets, while the former 
undergoes no such structural changes. 
On the other hand, the Fundulus egg is very sen- 
sitive to carbon dioxide. If a current of carbon dioxide is 
passed through the gas-chamber in which are contained the 
freshly fertilized Fundulus eggs, not a single cleavage occurs. 
Furthermore, the eggs which have resided for only four 
hours in such a current of carbon dioxide have lost their 
power of development for all time. This is of great impor- 
tance in judging of the effects of lack of oxygen—it points 
to the possibility that the resistance of the protoplasm to 
lack of oxygen is not so very different in the Ctenolabrus 
egg from that in the Fundulus egg, and that only a second- 
ary molecular change—the disintegration of the surface 
layer of the cells into a number of droplets—brings about 
a rapid destruction of the Ctenolabrus cells. 
This possibility is supported by another fact. I have 
pointed out in an article, which I have already cited, the 
remarkable indifference of the Fundulus egg to the concen- 
tration of the sea-water. This year Professor W. W. Nor- 
man made similar experiments in my laboratory upon the 
Ctenolabrus egg. In these it was found that the Ctenolabrus 
egg is almost as insensitive to an increase in the concentra- 
tion of the sea-water as is the Fundulus egg. 
T should not like to conclude this section without adding 
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