THE DIGESTIVE SYSTEM OF THE HOLOTHURIAN, CUCUMARIA ELONGATA. I. STRUCTURE OF THE GUT AND HEMAL SYSTEM

¹ Dove Marine Laboratory, University of Newcastle Upon Tyne, England

1. A system of nomenclature is given for the gut of Cucumaria elongata. The different regions of the gut have been named as follows: pharynx, esophagus, stomach, constriction, intestine I, intestine II, and cloaca.

2. The gut wall is composed of five distinct layers: (a) an outer serosal epithelium; (b) muscle cell bodies of the circular muscle fibers; (c) a muscle layer with outer circular and inner longitudinal fibers; (d) a connective tissue-fluid complex, the fluid component of which is continuous with the fluid in the hemal system; (e) the mucosal epithelium, which is composed of a single layer of tall slender cells.

3. Interspersed among the cells of the mucosal epithelium are mucous glands, secretory granules and gland cells. Mucous glands are present in the esophagus and constriction; secretory granules in the constriction, and gland cells in intestine I. Cells specialized to produce currents in the lumen of the gut are absent.

4. Stores of lipid are held in the cells of the mucosal epithelium and in the muscle cell bodies of the circular muscle fibers. Glycogen deposits have not been demonstrated.

5. The histology of the hemal system has been studied and the role of the hemal system in digestion is discussed.

6. From the distribution of gland cells and secretory granules it is suggested that the mucosal epithelial cells of the constriction and intestine I are sites of digestive enzyme production and secretion.

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