In $Pheretima$,the mouth develops from which of the following?

Enteronephric nephridia of earthworm are concerned with

Earthworm possesses how many pairs of hearts?

Define the following terms:
$(i)$ Endomysium
$(ii)$ Prostomium

Study the following in $Pheretima$.
$I.$ Dorso-intestinal blood vessels
$II.$ External intestinal plexus
$III.$ Internal intestinal plexus
$IV.$ Ventro-intestinal blood vessel
Arrange the blood vessels in the correct sequence of blood flow from the ventral blood vessel to the dorsal blood vessel.
The correct sequence is:

In earthworm,the dorsal wall of the intestine from the $26^{th}$ segment to $95^{th}$ segment forms a median internal fold called