Describe the nervous system of an earthworm.

(N/A) $\rightarrow$ The nervous system of an earthworm is ganglionated. Nerve cells unite to form ganglia.
$\rightarrow$ $A$ pair of ganglia is located on the ventral side in each segment after the $5^{\text{th}}$ segment. This is known as the ventral nerve cord.
$\rightarrow$ $A$ pair of ganglia is located on the ventral side in the posterior part of the $3^{\text{rd}}$ segment. It is known as the sub-pharyngeal ganglion.
$\rightarrow$ On the dorsal side of the pharynx,a pair of ganglia is located in the $3^{\text{rd}}$ segment,known as the supra-pharyngeal ganglion (cerebral ganglia).
$\rightarrow$ These ganglia are connected to the sub-pharyngeal ganglia through circum-pharyngeal connectives.
$\rightarrow$ The circum-pharyngeal connectives connect the sub-pharyngeal ganglia and the supra-pharyngeal ganglia to form a nerve ring.
$\rightarrow$ The cerebral ganglia,along with other nerves in the ring,integrate sensory input and command muscular responses of the body.