The adult Ascaris lumbricoides is a long whitish-pink cylindrical worm, tapering at both ends, curving ventrally in the male. Females reach 49 cm with a diameter of 3-6 mm. Males are much smaller, slightly more than half of the size of females.
Ascaris eggs vary widely in size and appear in two forms, fertilised and unfertilised (Figure 21.A,B). The fertilised egg is golden brown, ovoid, mammilated and 30-40 ^ wide x 50-60 ^ long, with a dense outer irregular shell and a more translucent regular inner shell. The thick external mammilated layer is often lost, giving a decorticate appearance. Evidence of segmentation or embryonation is often seen. The unfertilised egg is larger, more elongated and 40-50 ^ wide x 88-95 ^ long. The internal structure of the egg is poorly differentiated. Female worms produce up to 240000 eggs/day, which corresponds to just under 3000 eggs/gram of faeces (Mello, 1974). The egg shell is made up
of four layers: an outer mucopolysaccharide layer (Foor, 1967), a vitelline layer, a protein and chitin layer, and an inner selectively permeable layer consisting of an unsaponifiable lipid ascaroside (Perry and Clarke, 1982).
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