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Nervous System · The nervous system of earthworm is not well developed and is divided into the Central nervous system (CNS), Peripheral nervous system (PNS) and Sympathetic nervous system (SNS). a. Central nervous system (CNS) · Central nervous system passes through the centre of the body and consists of a brain ring that is present around the pharynx in segments 3 and 4.  · It is made up of: (a) two fused cerebral (Supra-pharyngeal) ganglia lying mid-dorsally and  (b) two fused sub-pharyngeal ganglia lying mid-ventrally. · The cerebral and sub-pharyngeal ganglia are connected by a ring-like circum-pharyngeal connective . Nervous system of Earthworm (a) Ventral nerve cord: It is paired, solid and show segmental ganglion from the 5th to the last segment. Each segmental ganglion is made up of two fused ganglia as evidenced by two segmental nerves that emanate from it. The nerve cord is made up of neurons and fibres and is covered by the visceral peritoneum and epineurium. Bipola...

Circulatory System and Circulation · Circulatory system of earthworms is of closed type as the blood flows in the closed blood vessels. · It consists of various types of blood vessels, heart, capillaries and  Plexi  which facilitate collection of the  deoxygenated  and the distribution of oxygenated blood to all organs and tissues of the body. · The blood contains the respiratory  pigment  called  haemoglobin  which is dissolved in the plasma. · Only one type of blood corpuscle, the  leukocytes  are present in the blood which kill the harmful germs. · No Red Blood Corpuscles (RBC) Present.  [BPKIHS 2005; IOM 2007; MOE] · Circulatory system  consists of three types of blood vessels- longitudinal, lateral or transverse blood vessels and intestinal plexus. I. Longitudinal blood vessels These function both as collecting and distributing blood vessels. These are  five  in number. a. Dorsal blood vessel · It is the...

Digestive System and Digestion · The digestive system of earthworm consists of the tubular alimentary canal and digestive glands associated with it. · Alimentary canal is a long straight tube with a variable diameter extending from mouth to anus. It consists of the following parts. a.  Mouth and Buccal cavity (1st to 3rd segments) b.  Pharynx (4th segment) c.  Oesophagus (5th to 7th segments) d. Gizzard (8th segment) e.  Stomach (9th to 14th segments) f.  Intestine (15th to the last segment except for anus) g.  Anus (last segment) · Digestion is the process of breaking down complex organic food by a biochemical process to change into a simple and soluble form to be utilized in the body. 1. Mouth and Buccal cavity The mouth is a  crescentic  aperture lying below the  fleshy lobe, the prostomium,  in  the peristomium . It leads into a short, narrow and thin-walled buccal cavity, extending up to the middle of the 3rd segment. The bucca...

· The generic name Pheretima was first coined by Kinberg (1867 AD). · The generic name Pheretima has been revised to Metaphire by Sims and Easton (1972 AD). · Earthworm is usually studied as a type of Annelida because it is easily available, harmless to handle, size is convenient and has well-known natural history and morphology. Systematic position of Earthworm: Kingdom: Animalia  Phylum: Annelida   Class: Oligochaeta (L. Oligos, few + Chaete, bristles)    Family: Megascolecidae     Genus: Pheretima or Metaphire      Species: posthuma Habits The earthworm has the following habits. 1. Feeding · It is  detritivores (feed upon decaying organic matter ) as well as an omnivore (feed on bits of plants and animal matter) · It takes soil by the sucking action of the pharynx . The organic particles in the soil are utilized and the undigested matter along with the soil is passed out as small p...