FIG. 1. A 3PN embryo fixed at the pronuclear stage. (a) Centriolar complex and sperm midpiece are closely associated with the nuclear
envelope ofone pronucleus (arrowhead). Two dense compact nucleoli are seen within the pronucleus. G, Golgi complex. (x7000.) (b) Centriolar
complex at higher magnification. The proximal centriole (C) is sectioned longitudinally and is obscured by osmiophilic centrosomal material.
Outer dense fibers are evident in the axonemal region of the midpiece (M). 0, ooplasm; P, pronucleus. (x70,000.)