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INTRODUCTIONThe current nomenclature for cells in the hepatopancreas of decapods is based on the classification of Jacobs (1928) and Hirsch & Jacobs (1928). They described the E-(embryonic), F-(fibrillar), B-(blister-like) and R-(resorptive or absorptive) cells. More recently the M-(midget) cell has been described (Al-Mohanna, Nott & Lane, 1984).Accounts of the structure of these cells are reviewed by Gibson & Barker (1979) and the B-cells most closely resemble those described and illustrated in this paper for the period 24 h after feeding.

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INTRODUCTIONIt is apparent, in a review on the decapod hepatopancreas (Gibson & Barker, 1979) that there is some consensus of opinion that the epithelium consists of E-, R-, F- and B-cells and M-cells (Al-Mohanna, Nott & Lane, 1985). Also, it is agreed that the gland produces enzymes and absorbs, digests and stores nutrients and excretes waste material. However, the apportionment of these functions to the different cells and the descriptions of the cytological processes involved are variously explained. Thus, the activity of proteases and amylases has been demonstrated in the secretion produced by the gland but the source of these enzymes is attributed to different cells and various modes of secretion are proposed. Also, no secretion granules of the zymogen type have been seen.There are probably two main reasons for the inconsistent interpretation of the activities of the cells. First, the different stages of the feeding and moult cycles are not taken into account and both these affect the cytology of the gland. Second, some of the functions have been deduced from observations of the fine structure without any experimental treatments to demonstrate more directly the processes involved. In the present work all the animals are taken at the same moult stage and observations are made throughout the feeding cycle. Also, aspects of the function are studied with markers which are administered in the diet and injected into the blood. The activities of hydrolytic enzymes associated with the different epithelial cells have been studied but these will be the subject of a separate publication dealing with the cytochemistry of the digestive processes.

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