Explain digestive tract of earthworm with diagram.

Explanation

The alimentary of earthworm is a straight tube and runs between first to last segment of the body. Mouth and prostomium : The first body segment on the earthworm anterior holds the mouth and prostomium resembling a lip is in the front of the mouth. It serves as a covering for the mouth and as a wedge to force open cracks in the soil into which earthworm may crawl. Mouth : Segments 1 to 3 form the mouth. It intakes food by coming out due to contraction of muscles joining body wall. Pharynx : Pharynx is located in 4th segment. Oesophagus : It is extended from 5th to 7th segment. Gizzard : It is a muscular structure located in 8th segment. Stomach : The stomach extends from 9-14 segments. Calciferous glands are present in the stomach, neutralise the humic acid present in humus. Intestine : Intestine starts from the 15th segment onwards and continues till the last segment. Intestinal caecae : A pair of short and conical intestinal caecae project from the intestine on the 26th segment. Typhlosole : The characteristic feature of the intestine between 26-35 segments is the presence of internal median fold of dorsal wall called typhlosole. (a) Pre typhlosolar region : The part of intestine extends upto origin of intestinal caecum is called Pre typhlosolar region. (b) Post typhlosolar region : The last part of intestine from 23 to 25 segments is without typhlosoles so it is called post typhlosolar region or anus. Typhlosole increases the effective area of absorption in the intestine. Digestion of food : The food of earthworm is decaying leaves and organic matter mixed with soil. This soil contains decomposing dead bodies, seeds, animal matter etc. Digestive enzymes breakdown complex food into smaller absorbable units. Undigested faeces are formed as globules in small heaps. It is known as wormcasting.