A Study of Eggs of Ascaris lumbricoides var. suum with the Electron Microscope

Abstract

Supports the general belief that the egg envelope is composed of 3 layers the chitinous shell which is formed first, followed by formation of the lipoid lining, and the outer protein coat added last. The protein coat of the egg, whose margin may be smooth or mammillated, appears as a dense, reticulated material with fibrils having a diameter of about 150 A. The chitinous shell, which is non-lamellated, is composed of highly branched microfibers which vary in diameter from approximately 75 A to 400 A. Both the protein coat and the chitinous shell are bordered by limiting membranes. Electron micrographs which may represent successive stages in the formation of the chitinous shell are presented. The lipoid layer of the living egg is striated; however, a suitable method for the fixation of this layer was not found. With respect to the perivitelline space, electron micrographs fail to reveal structure of any kind. The cytoplasm of the Ascaris egg is surrounded by a granular plasma membrane. Many granules and vacuoles are located within the very coarse cytoplasmic reticulum. The hyaline spheres, observed in immature eggs, are described.