Where is the head of the worm?

First, about what a head is. This is a part of the body, usually clearly defined, where the brain is located, the organs of vision, hearing, smell, and also the oral cavity are located. Now let’s imagine a worm. He has no head. His whole body is smooth, without the secretions of individual organs. But still, roughly speaking, you can distinguish in front of the worm, which can be called a head. If you take an earthworm, then the front can be distinguished by its characteristic belt, wider than the rest of the body. It is located just near the front of the worm.