The membranous structure of eggs of Ascaris lumbricoides as revealed by scanning electron microscopy.

The fine-structure of the egg shell and the oocyte of A. lumbricoides were examined with SEM. DMSO freeze fracture was used to obtain images of the eggs. Numerous filamentary fibers occur on the outer surface of the protein layer. These fibers are arranged in a network-like structure between the external projections of adjacent eggs. Twelve to 16 mammillated projections appear around the external periphery of each freeze fractured egg. Beneath the projection is a chitinous shell consisting of three layers; the outerlimiting membrane, the middle chitinous zone and the inner limiting membrane. Because the lipoid layer is dissolved by alcohol, it is not revealed with the freeze fracture technique. The oocyte is spherical or subspherical and possesses a continuous unit membrane. Particles, such as dense granules and refringent bodies, occur within the cytoplasm. Occasionally one or two first polar bodies, which will extrude into the perivitelline space, can be seen. The oocyte is frequently surrounded with a layer of deutoplasm.