How many baby earthworms emerge from a single cocoon of an earthworm?

Distinguish between the following: Septal nephridium and pharyngeal nephridium.

One very special feature in the earthworm $(Pheretima)$ is that

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

What is the function of the structure labeled $P$ in the given image?