Here's why:

* Excretion is the process of removing waste products from the body. These waste products are usually generated as a byproduct of metabolism.

* Body cells are the building blocks of our tissues and organs. They are essential for the functioning of our bodies.

Instead of being excreted, old or damaged body cells undergo a process called apoptosis, which is programmed cell death. Here's how it works:

1. Cellular signals: Cells receive signals indicating they need to die, such as DNA damage or lack of growth factors.

2. Caspase activation: These signals trigger a cascade of enzymes called caspases, which break down cellular components.

3. Cell shrinkage and fragmentation: The cell shrinks, its nucleus breaks down, and the cell fragments into smaller pieces called apoptotic bodies.

4. Phagocytosis: These apoptotic bodies are then engulfed and digested by other cells, such as macrophages, preventing inflammation and cell debris from accumulating.

Therefore, the process of removing old or damaged cells is not excretion but apoptosis and phagocytosis. This process is essential for maintaining tissue homeostasis and preventing the accumulation of damaged cells.