THE BIOLOGY OF THE CELL SURFACE 



Number of females 



Time in seconds to disinte- 

 gration of eggs exposed to 

 tap water during mem- 

 brane-separation 



10 



directed to the susceptibility of the egg to less dilute sea- 

 water at different stages of the process of membrane separa- 

 tion. In the experiment with the tap water it appeared 

 that when the egg cytolyzed, the break always came in that 

 part of the ectoplasm from which the membrane was lifting 

 at the time of exposure. However, the cytolysis induced 

 by tap water was far too rapid to allow exact observations 



Fig. 19. — Diagrams showing disruption of egg-contents at site of membrane- 

 separation in egg of Echinarachnius parma. a is a fertilized egg in which mem- 

 brane-separation has not begun. 



of this phenomenon. The experiments with less dilute 

 sea-water proved that the observation made during expos- 

 ure to tap water was correct: when eggs are exposed to 

 dilute sea-water during the period of membrane-separation 

 they cytolyze by an outflow of cytoplasm at the points from 

 which the membrane is lifting at the moment of exposure 

 (Fig. 19). Thus the susceptibility travels at the same rate 

 as the wave of membrane-separation. As stated above, 

 membrane-separation in the normal process results from 

 the solution of substances in the ectoplasm. Under the 

 microscope one can easily follow droplets of these as they 

 move across the perivitelline space before they completely 

 disappear. Any point on the egg-surface where this dis- 

 solution is taking place becomes the point of susceptibility 

 at the instant of exposure to dilute sea-water or tap water. 

 The most remarkable characteristic of this susceptibility 

 during membrane-separation is its sharp localization. I 



no 



