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Quarterly Journal of Microscopical Science, Vol s3-96, 517-537, Copyright © 1955 by Company of Biologists

Observations on the Stomach and Digestive Diverticula of the Lamellibranchia

I. The Anisomyaria and Eulamellibranchia

G. OWEN 1

1 Department of Zoology, University of Glasgow

A study of the digestive diverticula of the Anisomyaria and Eulamellibranchia revealed certain features hitherto undescribed. The diverticula consist of blind-ending tubules which open into ciliated main ducts by way of short, non-ciliated secondary ducts. The main ducts open into the intestinal groove. In all the species examined the ciliated epithelium of the main ducts was restricted to a well-defined groove, the remainder of the lumen being surrounded by a non-ciliated, brush-border epithelium.

Each tubule is surrounded by a system of smooth muscle fibres. Cilia associated with the darkly staining cells of the crypts were demonstrated in sections of the tubules. After feeding with titanium dioxide in suspension, this substance was later found in the large vacuolated cells of the tubules. The particles of titanium dioxide were larger than 0.1µ.

A continuous circulation is maintained within the main ducts solely as a result of ciliary activity. The exhalant current in the ciliated portion of the main ducts produces an inhalant counterpart current in the non-ciliated portion. It is suggested that fresh fluid is drawn into the tubules as a consequence of the absorptive functions of the large vacuolated cells. Indigestible material accumulates in the large vacuolated cells and is extruded into the main ducts where it is conveyed out of the diverticula by the exhalant ciliary current.

In both the Anisomyaria and Eulamellibranchia the flap-like major typhlosole prevents material entering the mid-gut except by the intestinal groove, and isolates the rejectory currents of the intestinal groove from the general circulation of particles in the stomach. In the Eulamellibranchia the major typhlosole also acts as a valve which controls the entry and exit of material into and out of the inhalant and exhalant portions of the main ducts.






© The Company of Biologists Ltd 1955