Sensory structures in Ascaris are

Options

A. Phasmids
B. Amphids
C. Papillae
D. All the above

Answer

To answer the question regarding the sensory structures in Ascaris, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Organism**: Understand that Ascaris is a genus of parasitic nematodes (roundworms) that inhabit the intestines of hosts.

2. **Recognize the Sensory Structures**: The sensory structures in Ascaris include:
- **Amphids**: These are sensory organs located on the head region of the worm. They are primarily chemoreceptors that help the organism detect chemical stimuli in its environment.
- **Phasmids**: These are similar to amphids but are located near the tail of the worm. They also function as chemoreceptors, allowing the worm to sense its surroundings.
- **Papillae**: These are small sensory structures found on the body of Ascaris. They serve as chemoreceptors and can also respond to tactile stimuli.

3. **Categorize the Types of Receptors**:
- **Chemoreceptors**: These receptors (amphids, phasmids, and papillae) respond to chemical signals, such as the concentration of carbon dioxide in the blood.
- **Tactile Receptors**: These receptors respond to touch and pressure but are less emphasized in the context of Ascaris.

4. **Conclusion**: Since all three structures (amphids, phasmids, and papillae) serve as sensory organs in Ascaris, the correct answer to the question is "all of the above."

### Final Answer:
The sensory structures in Ascaris are phasmids, amphids, and papillae; therefore, the correct answer is **all of the above**.

---