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Journal of Experimental Biology 2,373-388 (1925)
Published by Company of Biologists 1925

Studies on the Comparative Physiology of Digestion : III.--Secretion, Digestion, and Assimilation in the Gut of Ciona Intestinalis

C. M. YONGE B.Sc., Ph.D.¹

¹ Zoological Station, Naples, and the Department of Zoology, University of Edinburgh

1. The oesophagus is characterised by a great development of mucous glands and cilia, and its function is essentially that of transport.

2. The stomach epithelium contains many secretory cells and is in all probability the site of the elaboration of the digestive enzymes. There are no mucous cells.

3. The hind-gut possesses no secretory cells other than mucous cells. Large round or elliptical cells with prominent nuclei and cytoplasm colouring darkly with all glycogen stains are numerous and are also present occasionally in the stomach.

4. The hind-gut is the only part of the gut which possesses muscle-fibres in its walls, food being transported through the gut by ciliary action. Mucous cells are very plentiful and there are also secretory cells--quite unlike those of the stomach--whose function is problematic.

5. Starch, glycogen and sucrose are digested, the amylolytic ferment having an optimum temperature of between 42° and 43°C. and being destroyed at 64°C.

6. A lipolytic enzyme is present.

7. There is a very weak proteolytic enzyme which acts only in alkaline and neutral media with the formation of albuminoses, but there is no sign of amino-acids after 14 days' digestion.

8. The glucosides salicin and amygdalin are split up.

9. Absorption takes place primarily in the mid-gut, to a smaller extent in the stomach, and very slightly in the hind-gut.

10. The gut allows dissolved substances to diffuse through it in either direction, but the action of the epithelium causes fluid to flow out of the gut even against strong osmotic pressure.

11. Glycogen is found in the branchial sac, throughout the gut (except the sophagus) and in the ovary. It is most plentiful in the glycogen cells of the mid-gut and stomach. Fat is present in the sophagus, stomach, and ovary. Quantitative estimations show that the gut possesses the highest content of fat (including lecithin) and the ovary the highest content of glycogen.