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Quarterly Journal of Microscopical Science, Vol s2-83, 357-397, Copyright © 1942 by Company of Biologists
1 Department of Zoology, University of Bristol
1. The anatomy and histology of the alimentary canal, process of feeding, and physiology of digestion in Aplysia punctata have been investigated.
2. The food undergoes little trituration in the buccal cavity. The mode of action of the jaws and odontophore is adapted to the rapid intake of vegetable food.
3. The oesophagus and crop together form an anatomical and physiological unit.
4. Trituration occurs in the gizzard. The teeth are adapted to the trituration of plant material; this is of particular importance owing to the weak action of the cellulase.
5. Coarser particles of weed are retained by the teeth of the filter chamber and returned to the gizzard during the forward movement of the gut fluid.
6. The ciliary currents in the anterior intestine ensure that only food in a finely divided or fluid state is admitted to the stomach. Medium and larger sized particles are carried straight into the intestine.
7. Ciliary currents in the stomach are concerned with the removal of material rejected from the tubules of the digestive diverticula. This material is consolidated, cemented, and moulded into a faecal rod within the caecum, and conveyed by ciliary action to the intestine.
8. The intestine is concerned with the further consolidation and moulding of the complete faecal mass, and its propulsion (by combined ciliary and muscular action) to the rectum.
9. Mucus is secreted throughout the gut with the exception of the regions of the jaws, gizzard, and filter chamber. Enzymes are secreted in the salivary glands (amylase and protease) and in the digestive diverticula (carbohydrases, lipase, and proteases). Glands probably secreting a lubricant (other than mucus) occur in the epithelium of the lateral walls of the buccal cavity, and others, secreting a cementing substance, in the caecum and intestine.
10. Absorptive cells occupy the greater part of the epithelium of the digestive diverticula. They occur together with secretory, excretory, and storage cells.
11. Digestion occurs within the oesophagus and crop, gizzard, filter chamber, anterior intestine, stomach, and tubules of the digestive diverticula. The hydrogen ion concentration is here suitable for the action of the enzymes, and the gut fluid is kept in motion by the muscular activity of the walls.
12. A high pH exists in the lumen of the caecum, posterior intestine, and rectum, probably assisting in the consolidation of the faecal mass by increasing the viscosity of the mucus.
13. The presence of a highly efficient mechanism for the formation of the faeces is probably correlated with the poorly developed cleansing mechanism in the mantle cavity.
Note:
Owing to Dr. H. H. Howells's absence on active service, this paper, which represents the substance of the thesis he presented for the degree of Doctor of Philosophy, has been prepared for publication by Prof. C. M. Yonge.
