Final answer:
The collar or saddle-shaped structure that secretes mucus to surround fertilized eggs in earthworms is called the cl|itellum. It produces a membranous cocoon where fertilized eggs develop into baby earthworms.
Step-by-step explanation:
Earthworms, like many annelids, are hermaphroditic, meaning each individual possesses both male and female reproductive organs. Earthworm reproduction involves copulation, where two worms exchange sperm to fertilize each other's eggs. The process is essential for genetic diversity and the production of viable offspring.
The collar or saddle-shaped structure that secretes mucus to surround the fertilized eggs in earthworms is called the cl|itellum. The cl|itellum is a glandular ring of thickened skin that produces a membranous cocoon during the process of reproduction. Inside the cocoon, the fertilized eggs develop and give rise to baby earthworms.