Which structure in the alimentary canal of an earthworm is lined by an internal cuticle?

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.

Explain the process of mating and the formation of the cocoon in earthworms.

Earthworms increase the . . . . . . of the soil.

Give a scientific reason: The blood vascular system of leeches is also called the haemocoelomic system.

In which region is the tuft of nephridia found in earthworms?