_____posses very simple endocrine systems with few hormones whereas a large number of chemicals act as hormones and provide coordination in the _____

Answer

**Step-by-Step Solution:**

1. **Identify the Subject Matter**: The question pertains to the endocrine systems of different animal classifications, specifically invertebrates and vertebrates.

2. **Understand Invertebrates**: Invertebrates are animals that lack a vertebral column (backbone). They typically have simpler biological systems, including their endocrine systems.

3. **Characteristics of Invertebrate Endocrine Systems**: Invertebrates possess very simple endocrine systems with few hormones. Their glands are less complex and produce a limited number of hormones that regulate bodily functions. Examples of these glands include epithelial glands and optical glands.

4. **Understand Vertebrates**: Vertebrates are animals that possess a vertebral column. They have more complex biological systems, including their endocrine systems.

5. **Characteristics of Vertebrate Endocrine Systems**: Vertebrates have complex endocrine systems with numerous glands that secrete a variety of hormones directly into the bloodstream. Examples of these glands include the pituitary gland, thyroid gland, pancreas, adrenal glands, and gonads (testes and ovaries).

6. **Conclusion**: The statement can be completed as follows: “Invertebrates possess very simple endocrine systems with few hormones, whereas a large number of chemicals act as hormones and provide coordination in the vertebrates.”

**Final Answer**: Invertebrates possess very simple endocrine systems with few hormones, whereas a large number of chemicals act as hormones and provide coordination in the vertebrates.

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