Alimentary canal:
Ascaris has a straight alimentary canal from mouth to anus, consisting of mouth, pharynx, intestine and rectum.
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Important parts consist in the digestive system of ascaris
1. Mouth:
It is a triradiate aperture, guarded by three lips.
2. Pharynx:
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This is short, cylindrical, thick walled and muscular pharynx. The wall of pharynx consists of a syncytial epithelium traversed by radial muscles and containing glands.
Mouth and pharynx are lined internally by cuticle and ectoderm derived from embryonic stomodeum, and represents the foregut.
The lumen of pharynx is triradiate, each ray is a deep groove divide the pharynx into three sectors- dorsal and two subventral.
All the three sectors contain branched pharyngeal glands. Radial fibers of pharynx wall help in its expansion and marginal fibers help in preserving the triradiate form of lumen.
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3. Intestine:
The pharynx is followed by intestine which extends up to the length of the body and represents midgut.
The passage between pharynx and intestine is guarded by a valve to prevent regurgitation of the chyme.
The intestine is slightly dorso-ventrally flattened. Its wall consists of a single layer of tall columnar cells lined externally by a basement membrane and a thin layer of cuticle.
Columnar and absorptive endodermal epithelial cells bear microvilli (brush border) to increase the absorptive surface area.
4. Rectum:
Intestine is followed by a short rectum which too is a dorso-ventrally flattened structure. Wall of rectum consisting of columnar cells and lined internally by cuticle and externally by muscle tissue.
Thus the rectum forms from embryonic proctodaeum and represents the hind gut. In male, rectum opens into cloaca, while in female it opens out through anus.
