GENERAL HISTOLOGY

Detailed explanation-1: -Each tube foot consists of two parts: the ampulla and the podium. The ampulla is a water-filled sac contained in the body of the animal that contains both circular muscles and longitudinal muscle. The podium is the tube-shaped structure that protrudes from the body and contains longitudinal muscle only.

Detailed explanation-2: -The ampullae are connected to suckerlike podia. The entire structure is called a tube foot. In most cases, the small lateral canals connecting the ampullae to the radial canal are of equal length, so that the tube feet are arranged in two rows, one along each side of the groove.

Detailed explanation-3: -The madreporite leads to the stone canal which leads to the ring canal which has radial canals coming off of it that lead into each ray. Small lateral canals connect these radial canals to the tube feet.

Detailed explanation-4: -Protraction of the foot is made possible by the contraction of the ampulla musculature. The fluid within the ampulla cavity is driven into the podium which elongates by reason of the increased pressure within its cavity. During protraction the longitudinal muscles of the foot relax.

Detailed explanation-5: -The water vascular system is composed of canals connecting numerous tube feet. They move by alternately contracting muscles that force water into the tube feet, causing them to extend and push against the ground, then relaxing to allow the feet to retract.