PHYSIOLOGICAL EFFECTS OF LACK OF OXYGEN 379 



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 anaerobic. 1 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 



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. 



i Archive de biologic, Vol. XIII. 



