Explain the digestive tract of an earthworm with a diagram.

(N/A) $\Rightarrow$ The alimentary canal of an earthworm is a straight tube that runs between the first to the last segment of the body.
$\Rightarrow$ Mouth and prostomium: The first body segment of the earthworm contains the mouth. The prostomium is a lobe-like structure in 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 the earthworm may crawl.
$\Rightarrow$ Pharynx: The pharynx is located in the $4^{th}$ segment.
$\Rightarrow$ Oesophagus: It extends from the $5^{th}$ to the $7^{th}$ segment.
$\Rightarrow$ Gizzard: It is a muscular structure located in the $8^{th}$ segment,which helps in grinding soil particles and decaying leaves.
$\Rightarrow$ Stomach: The stomach extends from the $9^{th}$ to $14^{th}$ segments. Calciferous glands are present in the stomach,which neutralize the humic acid present in humus.
$\Rightarrow$ Intestine: The intestine starts from the $15^{th}$ segment onwards and continues till the last segment.
$\Rightarrow$ Intestinal caecae: $A$ pair of short and conical intestinal caecae project from the intestine on the $26^{th}$ segment.
$\Rightarrow$ Typhlosole: The characteristic feature of the intestine between the $26^{th}$ and $35^{th}$ segments is the presence of an internal median fold of the dorsal wall called the typhlosole. It increases the effective area of absorption in the intestine.
$\Rightarrow$ Digestion of food: The food of the earthworm consists of decaying leaves and organic matter mixed with soil. Digestive enzymes break down complex food into smaller absorbable units.
$\Rightarrow$ Undigested waste is excreted as globules in small heaps,known as worm castings.