THE NUTRITION OF PARANEMERTES PEREGRINA (RHYNCHOCOELA: HOPLONEMERTEA). II. OBSERVATIONS ON THE STRUCTURE OF THE GUT AND PROBOSCIS, SITE AND SEQUENCE OF DIGESTION, AND FOOD RESERVES.

1. Digestion in the hoplonemertean Paranemertes peregrina is achieved by a combination of extra- and intracellular processes. The extracellular phase, effected in an acidic medium, involves endopeptidases secreted by the gastrodermal columnar cells, and other, as yet unidentified, substances discharged from the intestinal gland cells. The semi-digested food is then phagocytosed and digestion completed intracellularly by peptidases, carbohydrases and lipases acting in harmony. Intracellular digestion is initially acid and then alkaline, with acid and alkaline phosphatases associated with the appropriate phases. 2. Nereids used as food are caught by the proboscis, and immobilized by secretions produced by the posterior proboscis gland cells. These secretions are pumped into the body of the prey via wounds caused by the central stylet. The nature of these secretions has not definitely been established, but they may contain the toxin anabaseine. 3. The anterior proboscis secretions are concerned with aiding the grip of the proboscis papillae and possibly with initiating the denaturation of the prey epidermis. 4. Acid secretions are produced by the foregut via a mechanism that does not involve carbonic anhydrase. 5. Other sites of enzymic activity have been reported, and where possible suggestions made as to their probable roles. 6. Fat forms the principal food reserve, with major deposits being stored in the gastrodermal columnar cells, but some glycogen is stored in a variety of body tissues.