CONTENTS

Experiments show that in Helix aspera amoebocytes repair a damaged shell after transporting calcium carbonate and proteins from other parts of the shell, or from the digestive gland. The mantle is firmly applied to the damaged area and over it exudes fluid rich in amoebocytes. These secrete, and rapidly calcify, a protein membrane. Similar additional calcified membranes give firm protection after 24 hours. The shell serves as a reservoir of calcium and protein, invaluable to a terrestrial gastropod. Amoebocytes can carry calcium back to the body. Extensive shell damage is repairable provided enough reserves remain: a snail cannot rebuild an entirely new shell. Thickening occurs whenever calcium and protein are available. Shell growth, however, initiated by the secretion of the periostracum, exclusively formed by the mantle skirt, happens only in conjunction with body growth. Provided feeding activities are normal, alkaline phosphatases are abundant during shell repair, especially around digestive gland lime cells. Shell repair and digestion are closely associated. Amoebocytes, ineffective in an active, starved snail, can re-peatedly repair damaged shell when a snail feeds, if only on filter paper: for onc