The alimentary canal or gut is basically a tube extending from anterior mouth to the anus. It is differentiated into a buccal cavity, pharynx, oesophagus, crop, gizzard and intestine. The mouth opens into a buccal cavity, a thin walled chamber lying in the first one or two segments of the body. Following the buccal cavity is a thick walled muscular chamber the pharynx is surrounded by a whitish mass of pharyngeal glands. The secretions of the pharyngeal glands are poured into the pharynx. The pharynx leads into an oesophagus, which is narrow tube, modified at the posterior as a crop and gizzard. The calciferous glands open into the oesophagus. The crop and the gizzard function as storage and grinding chambers respectively.The main characters of taxonomic importance in the alimentary canal are calciferous glands, gizzard or lamellae, beginning of the intestine, intestinal caecae, supra-intestinal glands and typhlosole.
Fig: Dorsal view of calciferous glands: A. Intramural; B. Extramural
Calciferous glands are associated with oesophagus. They are whitish, highly vascular organs provided internally with lamellae. Their shape, number, segmental position as well as whether they are stalked or sessile, paired or unpaired, external (etramural) or within oesophageal wall (intramural) provide useful distinguishing characters. In the absence of discrete calciferous glands, oesophagus may sometimes be markedly widened and provided internally with calciferous ridges or lamellae.
Fig: Dorsal view of calciferous glands in: A. Eudichogaster ashworthi; B.Octochaetona beatrix; C. Barogaster prashadi