The alimentary canal of frogs is short because they are carnivores.

Carnivores are animals that primarily consume meat. Their diet consists mainly of other animals, such as insects, spiders, small fish, and even other frogs. As a result, their digestive system has adapted to efficiently process and digest animal tissues.

There are several reasons why the alimentary canal of frogs is short, which can be explained in detail:

1. Efficient digestion:
- Frogs have a simple digestive system that allows for quick and efficient digestion of animal protein.
- The short alimentary canal reduces the time it takes for food to travel through the digestive tract, allowing for rapid absorption of nutrients.
- This is particularly important for carnivores as animal tissues require less processing and breakdown compared to plant matter.

2. Quick energy acquisition:
- As carnivores, frogs need to obtain energy quickly to support their active lifestyle.
- The short alimentary canal allows for rapid digestion and absorption of nutrients, ensuring a fast energy uptake.
- This is crucial for capturing prey and maintaining high metabolic rates.

3. Adaptation to a high-protein diet:
- Animal tissues contain high levels of protein, which is essential for growth, development, and maintenance of bodily functions.
- The short alimentary canal of frogs is specialized to efficiently extract and absorb proteins from their prey.
- Enzymes produced by the digestive system of frogs, such as proteases, are designed to break down proteins into smaller molecules for easier absorption.

In conclusion, the alimentary canal of frogs is short because they are carnivores. This adaptation allows for efficient digestion, quick energy acquisition, and effective utilization of the high-protein diet characteristic of carnivorous animals.