Observations on Feeding and Digestion in Glossobalanus minutus.

Abstract

ABSTRACT The epidermis and the digestive system of Glossobalanus minutus have been re-examined, and additional information obtained relating to their histology and function, and to the mode of feeding. The proboscis and collar constitute a simple ciliary mechanism which, aided by the current set up by the pharynx, enables the animal to take in material in suspension in the water or from the surface of the sand. It may thus be considered to retain the primitive ciliary feeding mechanism of the Chordata, although this is obscured in practice by the engulfing of sand associated with the burrowing habit. This retention probably accounts for the fact, recorded by previous workers, that the Enteropneusta frequently protrude their proboscis and collar from their burrows. The mobile lip of the collar provides a mechanism by which material can be prevented from entering the mouth; large particles can be seen to be rejected in this way. Suspended material can pass into the dorsal chamber of the pharynx, and collects in small masses which are rotated by ciliary action in the post-branchial chamber before being passed on. This is probably correlated with the fact that the external secretion of the proboscis contains a strong amylase which would pass into the pharynx with the food-material; the two would be mixed in the post-branchial chamber, and further secretions could be added from the latter. The distinction often drawn between a dorsal respiratory chamber and a ventral food chamber in the pharynx is thus not sound, although there is no reason to doubt that the organic content of the sand which passes into the latter can be utilized. The main cilia of the gill-arches are ‘lateral cilia’; short ‘frontal cilia ‘occur on the secondary arches, but their function could not he observed. The oesophagus produces a vesicular secretion which is discharged, often accompanied by nuclei, in cytoplasmic spherules. The epithelium of the ‘liver-sacs’ contain three main types of intracellular inclusion: colourless granular inclusions (believed to be a digestive secretion), brown granular inclusions, and large ovoid bodies with granular contents. The last develop at the distal end of the cells from minute vacuoles ; it is suggested that they may be excretory, although there is no definite evidence for this. All three types of inclusion are discharged from the cells, sometimes with nuclei. The intestinal epithelium is concerned with secretion, but to a much less extent than the sacs. The ovoid bodies and the brown inclusions are only produced in the latter. Evidence for the digestion of starch, glycogen, maltose, sucrose, casein, and triacetin is provided ; raffinose and inulin are not digested. Indications of the pH range of the amylase, protease, and lipase are given.