Fig. 2

Scanning electron micrographs of the surface of immature, mature and overripe eggs of P. pectinifera before and after fertilization. a An immature oocyte showing the projections of the follicle cells (FC, arrows) penetrating the vitelline layer (VL). b Polyspermic fertilization of an immature oocyte. Note the formation of the fertilization cones made by a large number of long microvilli protruding from the porous VL (arrows) and capturing the multiple sperm for their incorporation. c An oocyte treated with 1-MA for 50 min showing the VL without the openings characteristically present in the surface of immature oocytes in A. d The surface of a control egg fertilized at its optimal period of maturation (50 min 1-MA treatment) shows that, at variance with the multiple sperm penetration in immature oocytes shown in B, only the fertilizing sperm is captured by cytoplasmic protrusions emanating from the fertilization envelope (FE) (arrow). Note the different structure of the fertilization cone which is formed at this stage of maturation. e The structural modification of the VL of the overripe eggs makes this envelope more similar to that of immature oocytes and its openings. f Multiple sperm penetration (arrows) through the FE in an overripe egg upon insemination