390 



STUDIES IN GENERAL PHYSIOLOGY 



ture, it dies. If the experiment is interrupted early that 



is, when the cell-walls have just begun to become indistinct 



all, or at least a part, of the cell-membranes again become 



visible upon admission of air. Under these circumstances, 



however, every cell usually divides, not 

 into two, but into four cells which cor- 

 responds with what has been said before. 

 When we wait a little longer before 

 admitting air, a circular blastoderm is 

 at first formed in which no trace of cleav- 

 age is visible. The blastoderm then sud- 

 FIG. 112 denly breaks 



up into a large number of cells at 

 once, but curiously enough this 

 cleavage is confined, in most cases, 

 to the periphery of the blastoderm. 

 In this case also the refractive sub- 

 stance which has been described 

 plays a peculiar role. Figs. 112- 



17 represent 

 the various 



stages of the renewed cleavage of the 

 same blastoderm in which we studied 

 the disappearance of the lines of cleav- 

 age in hydrogen (Figs. 103-8). Fig. 

 108 shows the condition of the blasto- 

 derm in hydrogen at 2 :10 o'clock. Only 

 four large drops of the refractive sub- 

 stance, surrounded by droplets of smaller 

 size, permit one to recognize the place 

 of the blastoderm. At 2:18 pure oxygen was sent through 

 the gas-chamber. At first the smaller droplets separated 

 from the surface of the large droplets and moved toward 

 what had been the periphery of the blastoderm. (Previously, 



FIG. 113 



FIG. 114 



