The body cavity of a cockroach is called Haemocoel.

Explanation:
The body cavity, also known as the coelom, is a fluid-filled space that is found between the body wall and the internal organs of an organism. In the case of a cockroach, the body cavity is known as the Haemocoel.

The Haemocoel is unique to insects and other arthropods, and it plays a vital role in their physiology. It is a large, open cavity that is filled with haemolymph, which is the insect equivalent of blood.

The Haemocoel serves several important functions in the cockroach's body:

1. Circulation: The haemolymph in the Haemocoel acts as a circulatory fluid, transporting nutrients, hormones, and waste products between the various organs and tissues of the cockroach. Unlike in vertebrates, insects do not have a closed circulatory system with blood vessels. Instead, the haemolymph directly bathes the organs and tissues.

2. Immunity: The haemolymph also plays a crucial role in the cockroach's immune system. It contains various immune cells and molecules that help fight off infections and protect the cockroach from pathogens.

3. Respiration: Insects have a unique respiratory system that does not rely on lungs. Instead, they have a network of tiny tubes called tracheae that deliver oxygen directly to the cells. The haemolymph in the Haemocoel helps transport oxygen from the spiracles (openings on the sides of the body) to the tissues.

4. Locomotion: The Haemocoel provides a hydrostatic skeleton that helps in the cockroach's movement. The haemolymph, under pressure, provides support to the muscles, allowing them to function efficiently.

In conclusion, the body cavity of a cockroach is called Haemocoel. It is a fluid-filled cavity that serves vital functions such as circulation, immunity, respiration, and locomotion.

The body cavity of cockroach is called Heamocoel and is filled with blood..