Which part of the mammalian alimentary canal does not secrete any enzyme?

Options

A. Mouth
B. Oesophagus
C. Stomach and secrete dilute HCl
D. Duodenum

Explanation

To determine which part of the mammalian alimentary canal does not secrete any enzyme, we can analyze each option provided:

1. **Mouth**: The mouth is responsible for the initial stages of digestion. It contains salivary glands that secrete saliva, which includes digestive enzymes such as amylase (which breaks down starch into maltose) and lysozyme (which has antibacterial properties). Therefore, the mouth does secrete enzymes.

2. **Esophagus**: The esophagus is a muscular tube that connects the throat (pharynx) with the stomach. Its primary function is to transport food from the mouth to the stomach. Importantly, the esophagus does not secrete any digestive enzymes. It primarily uses peristalsis (a series of wave-like muscle contractions) to move food along. Thus, the esophagus does not contribute to the enzymatic digestion of food.

3. **Stomach**: The stomach is involved in further digestion and does secrete digestive enzymes. It produces gastric juice, which contains hydrochloric acid (HCl) and pepsinogen (which is converted to pepsin, a proteolytic enzyme). Therefore, the stomach does secrete enzymes.

4. **Duodenum**: The duodenum is the first part of the small intestine and plays a critical role in digestion. It receives bile from the liver and pancreatic juices from the pancreas, both of which contain various enzymes that aid in digestion. Thus, the duodenum does secrete enzymes.

Based on this analysis, the part of the mammalian alimentary canal that does not secrete any enzyme is the **esophagus**.

### Summary:
The part of the mammalian alimentary canal that does not secrete any enzyme is the **esophagus**.