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Fourteen species of marine invertebrates representing 12 phyla were kept in sea water containing NaHC(14)O(2) for 1 hour. All of them fixed CO(2) into acids of the Krebs citric acid cycle. In most species the major portion of the radioactivity recovered after chromatography was in succinic, fumaric, and malic acids. The findings favor the hypothesis that both CO(2) fixation and the citric acid cycle are virtually universal among marine invertebrates.

No abstract

It is thought (Willier ct a/., 1925;Jennings, 1957;Rosenbaum and Rolon, 1960a) that digestion in aquatic planaria is exclusively intracellular, occurring in the spherules of the phagocytic gastrodermal cells. There is, however, very little information concerning the formation of the spherules, the rate of digestion of their contents, and their ultimate fate. Data based on the rate of disappearance of alkaline phosphatase from the spherules in planarians which had been fed raw earthworms (Osborne, 1955) were inconclusive, because of the impossibility of distinguishing exogenous from endogenous enzyme. Nor was it possible in these studies to determine whether the uptake of nutrients occurs exclusively by the phagocytic action of the gastrodermal cells. A new approach to these problems was suggested by the experiments of Straus (1959) on the intracellular disposition of parenterally administered horseradish peroxidase in the rat. Peroxidase, which does not occur in most cells of animal organisms, is readily visualized histochemically and can be used as a tracer for exogenous protein.