. The Biological bulletin. Biology; Zoology; Marine biology. Figure 7. Six stages in the maturation of a digestive tubule cell: A, type A basophil cell; B, type B basophil cell; C, intermediate cell type; D, type B digestive cell; E. type A digestive cell; F, shedding of mature digestive cells. Region of acid phosphatase activity marked ap; b, basal vacuole; i, mid-cell inclusion; m, /3-metachromatic inclusion. that observed in digestive cells, which are known to be absorptive. Further, alka- line phosphatase was observed in the lumen of the ducts and duct ceca. an unex- pected site for an enz
. The Biological bulletin. Biology; Zoology; Marine biology. Figure 7. Six stages in the maturation of a digestive tubule cell: A, type A basophil cell; B, type B basophil cell; C, intermediate cell type; D, type B digestive cell; E. type A digestive cell; F, shedding of mature digestive cells. Region of acid phosphatase activity marked ap; b, basal vacuole; i, mid-cell inclusion; m, /3-metachromatic inclusion. that observed in digestive cells, which are known to be absorptive. Further, alka- line phosphatase was observed in the lumen of the ducts and duct ceca. an unex- pected site for an enzyme supposedly involved in transfer of extracellular sub- stances. It is possible that these enzymes are either utilized as extracellular hydrolytic enzymes or are involved in secretion of other hvdrolvtic enzymes at the cell membrane. Although it has often been suggested (hat fragmenting digestive cells con- tribute to extracellular digestion in the lamellibranch stomach (Mansour, 1946; Morton, 1956), experimental proof has been lacking. In the present study, histo- chemical evidence from Arctica islandica supported Mansour's hypothesis. In the lumina of the tubules, ducts, and duct ceca, recognizable cell fragments were found which stained diffusely for esterases, endopeptidases, and acid phosphatases. Histochemical reactions for all of these enzymes were far stronger in the digestive cell fragments than in the epithelium of the ducts, stomach, or midgut. By means of mechanical action in the stomach, the influence of amoebocytes. or pi 1 changes, these enzymes were released from the cell fragments to aid in extracellular digestion in the stomach. Neither cell fragments nor histochemical activity were recognizable in the midgut or in the feces. The histochemical demonstration of endopeptidases in the stomach lumen is interesting in light of the discovery of significant cathepsin B activity in the stomach of the lamellibranch Tresus capax (Reid and Rauchert, 1976) and the septi
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectb, booksubjectzoology
