PHYSIOLOGICAL EFFECTS OF LACK OF OXYGEN 391 



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. 113, 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 

 e 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 

 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 



FIG. 117 



