Bone marrow is not present in ?

Options

A. Mammals
B. Reptiles
C. Aves
D. Amphibians

Answer

To answer the question "Bone marrow is not present in?", we can follow these steps:

### Step-by-Step Solution:

1. **Define Bone Marrow**: Bone marrow is a semi-liquid material found in the hollow spaces of bones. It is responsible for producing blood cells, including red blood cells (RBCs).

2. **Identify Where Bone Marrow is Found**: Bone marrow is present in various classes of animals, including mammals, reptiles, and amphibians. It is located in the hollow areas of bones.

3. **Examine the Characteristics of Birds (Aves)**: Birds, classified as Aves, have a unique skeletal structure characterized by pneumatic bones. These bones are hollow and do not contain bone marrow.

4. **Compare Different Classes of Animals**:
- **Mammals**: Have bone marrow.
- **Reptiles**: Have bone marrow.
- **Amphibians**: Have bone marrow.
- **Birds (Aves)**: Do not have bone marrow due to the presence of pneumatic bones.

5. **Conclusion**: Based on the analysis, the correct answer to the question is that bone marrow is not present in Aves (birds).

### Final Answer:
Bone marrow is not present in Aves (birds).