The system which controls , regulate and co-ordinate the
functioning of all organ of the body is called as nervous system. In earthworm , nervous system is well developed and divided into following parts :
1. Central nervous system :
It consists of
ventral nerve chord lying ventrally to the alimentary canal in the middle line.
It starts from anterior end (from 3td segment) and extends throughout the whole
length of the body. It enlarges in each segment to form swelling called ganglia.
In the anterior end of 3rd segment or dorsal side of pharynx , there is
presence of bilobed swelling called cerebral ganglia or suprapharyngeal ganlia
which is also called the brain of the earthworm. The ganglia lies below the
suprapharyngeal ganglia is know as the sub-pharyngeal ganglia. In earthworm ,
supra-pharyngeal ganglia and circum-pharyngeal connective together form the
nerve ring. It lies in 3rd and 4th segment.
2.
Pheripheral
nervous system :
The nerve arising
from supra-pharyngeal , circum-pharyngeal , sub-pharyngral ganglia and
other segmental ganglia together form pheripheral nervous system. From cerebral
ganglia , 8-10 nerve arise which divide into branches that passes through
prostomium , pharynx and buccal cavity. From circum-pharyngeal ganglia 2 pair
of nerve arises which passes into buccal cavity and pharynx. From
sub-pharyngeal ganglia, three pair of nerve arises which passes into 2nd, 3rd
and 4rd segment. Behind 4rd segement , in each segment 3 pair of nerve arises.
Among them , 1 arise near anterior end of each segment and other 2 ftom the
swelling caled present in each segment of body of earthworm.
3. Autonomic nervous system : It consists of extensive nerve plexus
beneath epidermis in musculature of body wall and on alimentary canal.
nice post
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