Ambulacral System (OF ECHINODERMS)

The oval or actinal surface of star-fishes, sea urchins, etc., traversed by five double rows of locomotor suckers radiating from the mouth. The suckers pa out between a double series of calcareous plates, which are set vertically and transversely to the axis of the ray, and in star-fishes are sometimes called vertebral o icles. In the star-fish each row of suckers is really a zigzag, which gives each ray the appearance of having four rows of these ambulacral feet. Each sucker has at its inner end a sac (ampulla), and is connected with a water-tube which lies in a groove in the vertebral o icles, and radiates from a circular tube about the mouth, on which are ten polian vesicles and nine racemose vesicles and a stone-canal, ending on the aboral surface by the madreporite, sieve-plate, which admits water to the whole system.