Date of this Version
The egg of Ascaris has been widely used as a subject for cytological investigations. Nelson (1851) described the development of the egg of Ascaris nzystax. Leuckart (1886) and Wharton (1915) reported the Ascaris luinbricoides egg to be surrounded by a shell and an outer, albuminous layer. The appearance of unfertilized eggs of this species was described by Otto (1932) and Keller (1933).
The number of layers surrounding the egg of ascarids has been reported as three (Nelson, 1851, Ascaris mystax; Leuckart, 1886, Ascaris lumbricoides; Ackert, 1931, Ascaridia lineata; Wottge, 1937, Parascaris megalocephala ; Christenson, 1940, Ascaris lumbricoides ), four (Kreuzer, 1953, Ascaris lumbricoides ; Frenzen, 1954, Ascaridia galli , and five (Zavadovsky, 1928, Ascwis). A variety of techniques has been used by different authors in studying the egg layers, including microscopic observations of the penetration of substances into the egg, polarizing and fluorescent microscopy, centrifugation, and chemical tests on the membranes. The chemical composition of the layers has been investigated by several workers (Faurk-Fremiet 1913, 1913a; Chitwood 1938; Christenson, et al. 1942; Jacobs 1940; Timm 1950; MonnC and Honig 1954; Fairbairn 1955) and, in general, have led rather consistently to the conclusion that there are three membranes. Wottge (1937) described the endogenous formation of the egg layers of Ascaris megaloccphala , whereas Christenson (1940) believes the outer layer of the Ascaris egg to be of exogenous formation.
Morita (1953) examined paraffin sections of the egg shell of Ascaris megalocephala with the electron microscope and concluded that the layer "consists of completely individualized microfibrils." In the present investigation, thin sections were examined with the electron microscope to determine structural details of ova and the order of formation of the egg coverings of Ascaris lumbricoides var. suum.