The female genital aperture in earthworm is present ventrally on the segment: (in $^{th}$)

Earthworms are:

What is the function of the clitellum in $Pheretima$?

Match the regions of the earthworm based on the clitellum:
$P$ - Segments $14$ to $16$
$Q$ - Segment $17$ to the last segment
$R$ - Segments $1$ to $13$
Identify the correct sequence for the Pre-clitellar region,Post-clitellar region,and Clitellar region,respectively.

$Pheretima$ is:

The dorsal blood vessel of an Earthworm is: