The electron-microscopical observation of the egg of parasitic helminths was initiated by Morita (1953) being followed by Rogers (1956) and Inatomi (1957, 1960 a, b) who illustrated the structure of the egg shell in a number of nematodes.
The auther performed a serial comparative investigation of the ultra-structure of the egg shell in
Ascaris lumbricoides, Trichuris vulpis, Capillaria hepatica, Enterobius vermicularis, Ancylostoma duodenale, Trichostrongylus orientalis, Paragonimus westermani, Schistosoma mansoni, Clonorchis sinensis, Hymenolepis nana and
Taenia saginata.
From the data obtained the structure of the egg shell is to be devided in different five types.
A fine tubule system consisting of numberless fine caverns or capillaries is observed in the shell of eggs of which development is completed in a short period. This system is no more than a simple fine cavern in
Trichostrongylus orientalis, Ancylostoma duodenale which provide extremely thin egg shell and in
Enterobius vermicularis it is seen as plenty of capillaries in the outer layer.
The most well-developed tubule system is demonstrated in
Taenia saginata. The embryophore of this cestode is composed of five to six thousand of unique hexagonal blocks and not only the tubule system is developed in these blocks but the connecting parts of blocks play the role of capillaries.
A certain number of capillaries are developed in the egg shell in Schistosomes and numerous microvilli are seen being projected from the shell surface.
The etching shown on the egg shell surface of
Clonorchis sinensis is the interpretation of irregular-shaped coarse networks of delicate membraneous extuberances derived from the outer layer of the shell.
The eggs of
Paragonimus westermani and
Trichuris vulpis bear a single-layered thick shell and the outer surface of the shell is smooth.
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