What is the primary body cavity?

The primary body cavity is the space inside the animal’s body, between the body wall and the intestine, in which the internal organs are located. In roundworms, the primary body cavity formed by the ectoderm and endoderm is filled with a cavity fluid into which the intestines and genitals are immersed, plays the role of a hydroskeleton, and is involved in excretory and sexual functions. As the mesoderm develops, a whole forms – the secondary body cavity, lined on all sides by an epithelium of mesoderm origin. It first appears in annelids and is also filled with fluid and connected to the environment through the excretory system.

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