PHYSIOLOGICAL ErFrects oF Laok oF OxyGEN 3891 
during the liquefaction of the cell-walls, they had moved 
toward the center of the blastoderm.) 
At 2:35 a unicellular spherical blastoderm became visible 
(Fig. 112). The larger central drops gradually broke up 
into minute droplets, which often 
arranged themselves in a ring 
about the periphery of the blasto- 
derm (Figs. 118,114). Then forty- 
five minutes after the admission of 
oxygen, cleavage began. It occur- 
red only at such places where the 
FIG. 115 
tiny droplets have collected, 
namely, at the periphery. The 
periphery broke up into about 
eighteen cells at once (Fig. 
115). These cells about corre- 
FIG. 116 
spond in size with those 
found normally in the 
thirty-two to sixty-four- 
cell stages. The center of 
the blastoderm did not 
segment, with the excep- 
tion of one spot where the 
aie outlines of two cells be- 
came visible. I had noticed previously a small collection 
of the refractive droplets at this point. 
Still another relation between the distribution of the 
droplets and segmentation is noticeable. If the reader will 
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