MEMBRANE FORMATION AND CYTOLYSIS 



175 



Fig. 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. 



FIG. 39. Appearance of egg when first exposed to saponin solution at 

 9:07 A.M. 



FIGS. 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. 

 (If at this stage the egg is withdrawn from the influence of the saponin it can 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. 



