MEMBRANE FORMATION AND CYTOLYSIS 175 
Fig. 44 Fig. 45 
Formation of the fertilization membrane and cytolysis of the sea-urchin egg on 
treatment with saponin. 
: ae 39.—Appearance of egg when first exposed to saponin solution at 
: A.M. Z 
Fics. 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(if at this stage the egg is withdrawn from the influence of the saponin it can 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. ; 
Fics. 43, 44, and 45.—Advanced stages of cytolysis induced with saponin. 
