Excretory substances of animals contain _______ wastes.

Explanation

**Step-by-Step Solution:**

1. **Understanding Excretion**: Excretion is the biological process through which animals eliminate waste substances that are no longer needed and can be toxic to the body.

2. **Types of Excretory Processes**: Animals have different organs for excretion, including:
- **Kidneys**: They filter blood and excrete waste products through urine.
- **Lungs**: They expel carbon dioxide, a waste product of respiration.
- **Skin**: It excretes sweat, which contains waste substances.

3. **Identifying Excretory Substances**: The main type of waste that is removed from the body through the kidneys is nitrogenous waste. This includes:
- **Urea**
- **Uric Acid**
- **Ammonia**

4. **Conclusion**: Therefore, the excretory substances of animals primarily contain nitrogenous wastes.

**Final Answer**: Excretory substances of animals contain **nitrogenous** wastes.

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