1. DR. SHIVANI GUPTA,
PGGCG-11, CHANDIGARH

2. Phylum : Annelida Class Genus : Oligochaeta : Megascolex
Pheretima posthuma the common species of earthworm is usually given to kids for their biology experiments while studying the anatomy of earthworm.

3. Earthworm Biology that is metamerically segmented.
-The earthworm biology basically consists of an elongated, cylindrical body
that is metamerically segmented.
-A thin cuticle, epidermis and musculator makes up the body wall. The body cavity is a true coelon, as it is lined by the coelomic epithelium. There are four types of cells present in the coelomic fluid, phagocytes, mucocytes, round nucleated cells and the chloragogen cells.
-The circulatory system of earthworm is closed type that is made up of blood vessels and capillaries that are fork out all over the body. The plasma and corpuscles make up the blood and it has multiple hearts.
-The earthworm is a hermaphrodite and reproduction is strictly sexual. The nephridia is distinguished into three types namely, pharyngeal, integumentary and the septal nephridia.
-The earthworm has a very well developed nervous system that consist of a simple brain and nerve cord. In this article on earthworm digestive system we will understand the earthworm digestive system in order.

4. A fully grown earthworm measures about 150mm in length and 3-5mm width The body is cylindrical and elongated. The anterior end is pointed , while the posterior end is rounded.

5. EARTHWORM Body Segments Prostomium Peristomium
•14-16 segments: Clitellum Glandular tissue covering
•Metameres
•Dorsal side- dark mid dorsal line
•Ventral side- genital
openings
•Ant. End- Mouth, Prostomium, Peristomium

6. Body apertures Spermathecal Pores Female genital Pores
Nephridiopores
Dorsal pores
Anus

7. Internal Morphology

8. Digestive system
An earthworm eats dead and decaying plant and animal matter and dirt present in the soil. Let us see the various organs of the earthworm digestive system in order:
The mouth- The prostomium or mouth of an earthworm is made up of strong lips. The buccal cavity is made up of 2½ segments that is thin walled and shaped like a pear. There are no jaws and teeth and the earthworm sucks in the soil containing food with the muscular pharynx. The lips break the food into smaller pieces and use tiny soil particles to help them grind the food into smaller bits. Once the food is 'chewed', the food travels down to the pharynx from the mouth.
Pharynx -The food is lubricated with the mucus secretions on the pharynx that helps it pass easily to the esophagus. The pharynx is made up of 1½ segments and there is cerebral ganglion present between the buccal cavity and pharynx. The lateral wall invaginates, the salivary chamber present in the dorsal side and there is a ventral conducting chamber.
The pharynx saliva contains mucus and proteioltyic enzyme that
begins the digestion of proteins in the pharynx.

9. Digestive System
Esophagus -The food is then passed on to the esophagus that is present in
the 5th to 7th segment. The esophagus is like a small tube that has calciferous glands. These glands release calcium carbonate that helps neutralizing the acids formed in the decayed food matter and remove excess of calcium from the earthworms body. The food then moves into the next chamber called the crop.
Crop -The crop is where the food is stored till it can be moved to the next chamber, the gizzard
Gizzard -The gizzard is like a strong muscular food processor. It is also called the proventriculus and is found in the 8th segment. There are powerful muscles in the gizzard that mix and churn the food to pulpy mass of food and dirt. The food is grind with the help of stones present in the gizzard. There are enzymes secreted from the walls of the gizzard that help in the digestion, that is, chemical breakdown of the organic matter ingested. The thick paste so formed is then pushed into the intestine.

10. Digestive System
Intestine-The intestine contains bacteria that help in further breakdown of the food. The bacteria act on the food releasing vitamins, proteins, carbohydrates and minerals in the worm body to help it survive. The intestine is present from the 15th to 120th segment, that is, most of the worms length. The intestinal ceacea present up to the 22nd segment, secrete intestinal juice containing amylase, amylopsine, sucrase, maltase, chitinase, lipase and proteiolytic enzymes. The digestion takes place in the pre- tryphlosolar part, that is present in the 15th to 26th segment. The waste matter or faecal matter is formed in the typhlosolar part present from the 94th to 120th section.
Anus- The intestine opens outside the body through the anus.

11. Circulatory System
As food is digested, the blood in the circulatory system picks it up for distribution to all the cells of the body. In simpler we have studied so far, the digested food had only to diffuse a short distance in order to reach all cell of the body. But in higher forms, the distances are greater, and more food
material is needed by the many specialized and active cells of the body. The blood of the earthworm moves through a series of closed tubes, or vessels. It flows forward to the anterior end in a dorsal blood vessel and moves to the posterior end in a ventral blood vessel. Small tubes connect the dorsal and ventral vessels throughout the animal, except in the segments 7 and 11.
Here there are five pairs of connecting tubes which are large and muscular. By means of alternate contraction and relaxation,they keep the blood flowing. Not true hearts, they are called aortic
arches.
In earthworm ,the circulation is closed type.The circulatory system consists of heart, blood vessels, capillaries and blood glands

12. Excretory System The earthworm absorbs oxygen and
gives off carbon dioxide through a thin skin. This skin is protected by a thin cuticle secreted by the epidermis and kept moist by a slimy mucus also produced by epidermal cells. A moist surface is necessary for oxygen to be absorbed and carbon dioxide to be given off. If the worm is dried by the sun, it will die because the exchange of gases can no longer take place.
Nitrogen-containing waste materials from cell activities are removed to the outside of the body by little tubes.
There are two such structures, called nephridia, in each segment except the first three and the last.

13. Nervous System
The earthworm has a simple yet sensitive nervous system. Its cerebral ganglion, or brain, is connected to the ventral nerve cord, which runs the length of its body. At each segment, segmental ganglion branch off from the ventral nerve cord, thus connecting every segment to the earthworm's brain. Each segmental ganglion must be well coordinated with each other since they must interact in order to control muscle contractions in each segment that are responsible for locomotion.

14. Reproductive system Earthworms are hermaphrodites
with complex male and female reproductive organs present in each individual, but they cross
fertilize. Two earthworms mate by attaching at their clitella and exchanging sperm, and then they separate. The received sperm are temporarily stored in sperm receptacles while the clitellum secretes a mucous cocoon. The cocoon slides along the worm, picking up the eggs which are produced in ovaries and then the stored sperm from special reproductive pores (female and male gonophores), and then slips off the worm's head. The embryos develop within the cocoon.

15. Reproductive system
The reproductive structures of the earthworm start at segment
nine. Identify the seminal receptacles (bulb-like organs in segments nine and ten) where sperm received from another worm are stored, and the three pairs or whitish seminal vesicles (segments 9-12). Sperm are produced within testes located inside the seminal vesicles and transferred to the male gonophores via the vas deferens. The female reproductive structures consist of a pair of ovaries (segment 13) connected to the female gonophores via a series of small passageways.

16. Cocoon formation

17. Cocoon formation