What are gemmules?

Explanation

**Step-by-Step Text Solution:**

1. **Definition of Gemmules**: Gemmules are specialized structures found in freshwater sponges that serve as a means of asexual reproduction.

2. **Formation of Gemmules**: In freshwater sponges, the parent sponge releases a mass of cells. This mass is not just a random collection of cells; it is a specialized grouping that is designed for survival and reproduction.

3. **Enclosure of Cells**: The mass of cells released by the parent sponge is enclosed in a protective, opaque envelope. This envelope helps protect the cells from environmental stresses and predators.

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