STUDIES ON FEEDING, DIGESTION, AND FOOD STORAGE IN FREE-LIVING FLATWORMS (PLATYHELMINTHES: TURBELLARIA)

¹ Department of Zoology, The University of Leeds, England

1. A study has been made of the food, feeding mechanisms, digestion and food storage in the triclad Polycelis cornuta, supplemented by observations on representatives of the other three flatworm orders.

2. Each form has a characteristic method of feeding, but in general the range of available prey has been greatly increased by elaborations in the structure and use of the pharynx. Mucus plays a minor part in feeding, except for the "snares" of the triclad. Rhabdoid material has no function in feeding. It forms a temporary cuticle and in polyclads a covering for the eggs.

3. In Polycelis mechanical breakdown of the food is followed by phagocytosis into the gut cells and intracellular digestion. Elsewhere the preliminary breakdown may be wholly or in part enzymatic; only in Cycloporus is there purely intraluminar digestion with absorption in place of phagocytosis.

4. Polycelis can make use of all three food elements, and stores of each type normally occur. In the other forms food storage is less well developed though reserve fat at least is usually to be found.