PHYSIOLOGICAL EFFECTS oF Lack or OxyGen 3879 
Fundulus which showed that the egg not only segments 
when oxygen is removed by pyrogallol, but even continues 
to develop for about sixteen hours. Demoor, who was un- 
familiar with my experiments, began experiments on Trades- 
cantia cells in which he found that a cell-division which had 
already started at the time that the oxygen was being 
removed continues to the completion of nuclear division, 
but that the subsequent cell-division does not occur. He 
concludes from this, first, that cell-division is impossible 
without oxygen, and especially that without oxygen the cell- 
membrane cannot be formed; and, secondly, that the nucleus 
may divide without oxygen, that it is anaérobic.' I have in 
a previous paper pointed out the incorrectness of the second 
conclusion. 
My own experiments, which I will give here, were made 
on fish eggs (Ctenolabrus and Fundulus) and sea-urchin 
eggs. 
The egg of Ctenolabrus, a marine Teleost, is perfectly 
transparent and free from pigment, and the changes which are 
described in the following pages can be studied with great 
accuracy under the microscope. The eggs which were used 
in the following experiments were always fertilized artificially 
in the laboratory. 
If the freshly fertilized eggs of Ctenolabrus are intro- 
duced. into an Engelmann chamber, and care is taken that all 
the air is driven out of the apparatus before the experiment 
is begun, and the stream of gas is maintained, the eggs 
cleave, without exception, into two cells, and in most cases 
even into four cells. Occasionally they even go into the 
eight-cell stage. If the eggs are introduced into the gas- 
chamber not immediately after fertilization, but in one of 
the later stages of cleavage, two or three divisions of all the 
cells still occur. 
1 Archive de biologie, Vol. XIII. 
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