The common prostate and spermatic duct of earthworms is known as vasa deferentia.

Explanation:
Earthworms are hermaphroditic organisms, meaning they have both male and female reproductive organs. The male reproductive organs in earthworms include the testes, vasa deferentia, seminal vesicles, and accessory glands.

1. Testes:
The testes are the primary male reproductive organs in earthworms. They are responsible for producing sperm cells.

2. Vasa Deferentia:
The vasa deferentia are the common prostate and spermatic duct in earthworms. They are a pair of tubular structures that connect the testes to the seminal vesicles. The vasa deferentia transport the sperm cells from the testes to the seminal vesicles, where they are stored before being released during copulation.

3. Seminal Vesicles:
The seminal vesicles are sac-like structures that store the sperm cells produced by the testes. They receive the sperm from the vasa deferentia and also secrete seminal fluid, which provides nourishment and protection to the sperm.

4. Accessory Glands:
Earthworms also have accessory glands that contribute to the production of seminal fluid. These glands include the prostate glands, which secrete additional fluids to the seminal vesicles.

5. Copulatory Apparatus:
Earthworms have a complex copulatory apparatus that allows for the exchange of sperm between individuals during mating. The vasa deferentia play a crucial role in this process by transporting the sperm from the testes to the seminal vesicles, where they are stored and eventually released.

In conclusion, the vasa deferentia in earthworms are the common prostate and spermatic duct that transport sperm from the testes to the seminal vesicles. They are essential for the reproductive process in these hermaphroditic organisms.