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 104. 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 
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