of controlling the amount of water in the body is called as
“osmoregulation”.
6.1 (b) Excretion in Earthworm :
In earthworm, the excretory organs are nephridia. The internal funnel-
like opening is called as “nephrostome”. The waste material from body
cavity (coelom) enters the nephridium through nephrosome. In the inner
lining of nephridium, the cells absorb useful substances like glucose.
6.2S TRUCTURE OF A TYPICAL NEPHIRIDIUM :
A typical nephridium consists of three pars : nephrostome, body and
terminal duct. The nephridium communicates with the coelom (body
cavity) through internal nephrostome. Nephrostome is a ciliated funnel
which leads into body of nephridium through the neck. The body of
nephridium consists of short straight lobe, a long spiral lobe with
narrow apical part. Spiral lobe consists of proximal limb and distal limb.
Neck of the nephridium leads into proximal part of spiral lobe and
terminal duct leaves the proximal limb. The tubule of the neck enters
the body of the nephridium and leaves the body as terminal duct. These
tubules have ciliated tracts inside. The number of ciliated tracts depends
upon the number of coils of the tubules. The terminal duct may open
outside by nephridiopore or into the gut (alimentary canal).
