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Summary.

A simpler nomenclature is suggested for the parts of the holothurian gut. The rete mirabile of Holothuria forskali showed three regions, namely, a relatively unpigmented region attached to the dorsal edge of the stomach which connected by a single strand to a yellowish-brown region alongside the intestine which had a brownish-black edge to it filled with melanin granules. Feeding with iron carbonate saccharated showed that some amoebocytic ingestion took place in the stomach and intestine and clumps of amoebocytes containing iron appeared in the haemal canals, lumen of the rete mirabile and in the walls of the respiratory trees, where it was probably egested. Injection of trypan blue into the body cavity resulted in its phagocytosis by the agranulocytes and their clumping together with the granulocytes in all the soft-skinned organs within the cavity especially on the respiratory trees, gonads and intestine. Migration into the lumen of the latter was observed. Melanin granules were identified within granulocytes in the lumen and walls of the rete mirabile as well as in the cells of the rete wall.