The nervous system is well developed in an earthworm.It consists of central, peripheral and autonomic nervous system.
The central nervous system consists of nerve ring and nerve cord.
It consists of a pair of supra- pharyngeal ganglia, circum pharyngeal, and sub pharyngeal ganglia.
The central nervous system consists of a pair of cerebral ganglia or supra-pharyngeal ganglia which fuse to form brain which is whitish pear-shaped structure lying in the 3rd segment in the group between buccal cavity and pharynx dorsally.
Circum pharyngeal connectives:
Circum pharyngeal connective is a thick structure which runs backward and downward laterally encircling the pharynx to join with sub pharyngeal ganglia, a pair lying in the 4th segment below the alimentary canal.
Sub pharyngeal ganglia:
The sub pharyngeal ganglia lie ventral to the alimentary canal in the 4th segment which is small and formed by a pair of ganglia. From this, a ventral nerve cord runs towards the posterior region and each segment form a swelling like structure called segmental ganglia.
The peripheral nerves are mixed because they are afferent and efferent.The arise from central nervous system and supply all other body structures. From the cerebral ganglia,8-10 nerves originated supply the prostomium and buccal chamber. From the circum pharyngeal, connective nerves are supplied to peristomium and buccal chamber, from the sub pharyngeal ganglia nerves originate and supply to 2nd, 3rd, 4th segment. From each segmental ganglia, 3 pair of nerves originates which supply body wall, gut wall, septa, septal nephridia.
The autonomic nervous system controls all the involuntary activities of the body.The nerve arises from circum pharyngeal and they form a network-like structure like plexus in the body wall and gut wall.