384 STUDIES IN GENERAL PHYSIOLOGY 



is inaugurated. This marked retardation of cell-division 

 has its basis in peculiar molecular changes, which we will 

 discuss in detail in the following sections of this paper. 



IV. THE FUSION OF CLEAVAGE -CELLS THROUGH LACK OF 



OXYGEN 



The fact that the egg of Ctenolabrus is not able to seg- 

 ment without oxygen may be due to one of two causes: 

 first, processes of oxidation might be the only source of 

 energy for segmentation; second, it might be possible that, 

 even though enough chemical energy for segmentation can 

 be obtained from hydrolysis, yet this chemical energy 

 cannot be connected with the chemical energy necessary 

 for cleavage because of the structural changes brought 

 about by the lack of oxygen. Demoor concludes from his 

 experiments on Tradescantia that no cell-wall is formed 

 without oxygen, and that in consequence no cell-division 

 occurs without oxygen. Demoor brings no positive proofs for 

 his view. In the case of the Ctenolabrus egg, however, we can 

 show that structural changes occur in cleavage-cells, in con- 

 sequence of which these cells fuse together. It is conceiv- 

 able that the same structural changes must also hinder the 

 segmentation of the freshly fertilized egg. The sketches, 

 Figs. 103-8 were made with the camera lucida and were all 

 taken from the same egg. The egg was fertilized at 10 A. M., 

 and immediately thereafter introduced into a gas-chamber 

 and kept in a current of hydrogen. Cleavage took place in 

 the normal way, and since the current of hydrogen was not 

 very strong, even the eight-cell stage was reached (Figs. 

 103-5). A series of degenerative changes then set in. At 

 first a gathering of the strongly refractive droplets, which 

 we have described already, was formed in the two main 

 furrows (Figs. 104 and 105) and some furrows began to be- 

 come indistinct. Fifteen minutes later the greater portion 



