Which of the following mammals lacks corpus callosum

Options

A. Ornithorhyncus
B. Balaenoptera
C. Macropus
D. Macaca.

Answer

To determine which mammals lack the corpus callosum, we can follow these steps:

### Step 1: Understand the Corpus Callosum
The corpus callosum is a band of nerve fibers that connects the left and right cerebral hemispheres in the brain. It allows communication between the two sides.

### Step 2: Identify Mammal Categories
Mammals can be categorized into three main groups:
1. **Monotremes**: Egg-laying mammals (e.g., platypus).
2. **Marsupials**: Mammals that give birth to underdeveloped young and carry them in pouches (e.g., kangaroo).
3. **Placental mammals**: Mammals that give birth to more developed young (e.g., humans, whales).

### Step 3: Determine Presence of Corpus Callosum
- The corpus callosum is typically present in placental mammals.
- It is generally absent in monotremes and marsupials.

### Step 4: Analyze the Given Options
1. **Ornithorhynchus (Platypus)**: This is a monotreme and lacks a corpus callosum.
2. **Velenotera (Blue Whale)**: This is a placental mammal and has a corpus callosum.
3. **Macropus (Kangaroo)**: This is a marsupial and lacks a corpus callosum.
4. **Macaque (Monkey)**: This is a placental mammal and has a corpus callosum.

### Step 5: Conclusion
Based on the analysis, the mammals that lack the corpus callosum are:
- **Platypus (Ornithorhynchus)**
- **Kangaroo (Macropus)**

### Final Answer
The mammals that lack the corpus callosum are the **platypus** and the **kangaroo**.

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