The life cycle of Pheretima, commonly known as the earthworm, is quite fascinating, especially considering it’s a hermaphrodite, meaning each individual possesses both male and female reproductive organs. However, self-fertilization is usually avoided, and cross-fertilization is the norm.

The process begins with copulation, where two earthworms align themselves in opposite directions, ventral surfaces together. They exchange sperm, which is stored in the spermathecae of each worm. Following this, the clitellum, a thickened glandular segment on the earthworm's body, becomes highly active. It secretes a mucoid band that hardens into a tough, protective structure known as a cocoon.

As the cocoon slides forward over the worm's body, it collects the worm's own eggs (from the ovaries) and the stored sperm from its partner. Fertilization thus occurs within the cocoon. Once the cocoon slips off the anterior end of the worm, its ends seal, forming a protective capsule. Inside this cocoon, the embryos develop, feeding on albumin secreted by the clitellum.

After a period of incubation, typically a few weeks to months depending on environmental conditions, several juvenile worms hatch from the cocoon. These young worms are miniature versions of the adults, lacking a clitellum initially. They grow and mature, eventually developing their own clitellum and reaching reproductive age, thus completing the cycle. The entire process is a remarkable adaptation for terrestrial life, ensuring the survival and propagation of these vital soil dwellers.

Here's a simplified diagram of the Pheretima life cycle: