Membrane Formation and Cytolysis 



175 



Pig. 39 



Fig. 40 



Fig. 41 



Fig. 42 



Fig. 43 



Fig. 44 



Fig. 45 



Formation of the fertilization membrane and cytolysis of the sea-urchin egg on 

 treatment with saponin. 



Fjo. 39. — ^Appearance of egg when first exposed to saponin solution at 

 9:07 A.M. 



FioB. 40, 41, and 42. — Formation of fertilization membrane. The stage of 

 completed membrane formation as depicted in Fig. 42 was reached at 9:15 a.m. 

 fif at this stage the egg is withdrawn from the influence of the saponin it can 

 develop.) Cytolysis (Fig. 43) began at 9:20 a.m. 



Figs. 43, 44, and 45. — Advanced stages of cytolysis induced with saponin. 



