Explain the nephridia of an earthworm.

(N/A) In earthworms,the excretory organs occur as segmentally arranged coiled tubules called nephridia. They are of three types:
$(i)$ Pharyngeal nephridia: These are located in segments $4$,$5$,and $6$.
(ii) Integumentary nephridia: These are attached to the lining of the body wall of segment $3$ to the last,which open on the body surface.
(iii) Septal nephridia: These are present on both sides of the intersegmental septa of segment $15$ to the last,which open into the intestine.
There are no nephridia present in the first two segments.
Integumentary nephridia excrete the excretory substances onto the body wall. This type of excretion is called exonephric excretion.
Pharyngeal and septal nephridia discharge the excretory substances into the alimentary canal (buccal cavity and intestine). This type of excretion is called enteronephric excretion.
These different types of nephridia are basically similar in structure. Nephridia regulate the volume and composition of the body fluids.
$A$ nephridium starts as a funnel that collects excess fluid from the coelomic chamber. The funnel connects with a tubular part of the nephridium,which delivers the wastes through a pore to the surface of the body wall or into the digestive tube.