VITELLINE MEMBRANE 

 -CORTICAL LAYER 

 — EN OOPLASM 



VITELLINE 

 MEMBRANE 



CORTICAL 

 GRANULE 



PLASMA 

 SURFACE 



_,_____^^VITE LLI NE 

 \ -X^" MEMBRANE 

 ^^^-'"^==^0 R T I C A L 

 _^^^^ GRANULES 



" P L A S M A 

 2 S U R FACE 



FE RT IL IZ AT ION 

 MEMBRANE 



PLASMA 

 SURFACE 



Fig 129 Formation of the fertilization membrane in the mature egg of the sea urchin. 

 (A) Surface of the egg and surrounding jelly coat before fertilization. (After Runnstrom, 

 '49 p 245 ) (Bl 2 3 4, 5) Point x marks the point of sperm contact. The fertilization 

 membrane separates 'from the egg at the point of sperm contact and spreads rapidly 

 around the egg from this point. (After Just, '39, p. 106.) (C) Membrane forma ion m 

 greater detail (After Runnstrom, '49, p. 276.) ( 1) As the vitelline membrane is l.f ed 

 off from the plasma surface of the egg, cortical granular material is exuded from the 

 egg cortex and passes out across the perivitelline space toward the fertilization mem- 

 brane (2) Cortical granules begin to consolidate with the vitelline membrane. (3) 

 Fully developed fertilization membrane is formed by a union of the vitelline membrane 

 with the cortical granules derived from the egg cortex. 



258 



