Which insulates various internal organs from the stresses of body-wall movement and bathes them in a liquid through which nutrients and waste products can diffuse?

Coelom.

Explanation:

The coelom is the body cavity prtesent in the animals that contains digestive organs and other parts of body. The coelom cavity is lined by the mesothelium.

The main function of coelom is the insulation of the internal organs. This cavity protects from the stress of body-wall movement and bathes them in the liquid solution. The liquid consists of dissolved nutrients and waste can easily be diffuse in the liquid.

Thus, the answer is coelom.