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The digestive gland of Pecten muximus consists, as in other lamellibranchs, of numcrous blindcnding tubules which communicatc with the stomach by partially ciliated main ducts and non ciliated secondary ducts. Thc non-ciliated cells of the main ducts arc charactcrizcd by a well developed brush border constituted by high and dcnsc microvilli and a strong pinocytotic activity. Ciliatcd and non ciliatcd cclls havc a very similar fine structure. The digcstivc tubulcs have a large lumen and contain digestive cells at diffcrcnt stagcs of absorption , digestion and excrction, onc part of thc tubules being functional while the other is disintcgrating. Thc dark crypts contain the flagellated secrctory cclls, charactcrizcd by a well developed granular cndoplasmic rcticulum, and the young immature cells which may replacc both thc sccretory and digestive cells. The numerous lipid droplcts occurring in thc digestive duct cells and in the digcstivc cclls rcvcal the lipid storage function of the digestivc gland. Several enzyme activitics involvcd in digestion have been localized in the digcstivc gland. High amylase activity and cellulase and lysozyme activitics have been found in the ducts and in the tubules, whcrcas no protcolytic activity could be detected histochemically. Somc intraccllular peptidases and glycosidases have been localized in thc cclls of the digestive gland, especially in the brush-bordcr cclls of the ducts and in the functional part of the tubules. High alkaline and acid phosphatase activities are displaycd by the duct brush-border cells and the digestive and secretory cclls. These results show the main role of the digestive gland, both in cxtracellular digestion (secretion of thc digcstivc enzymes) and in absorption and intracellular digestion and providc information on the respective functions of thc different cells within these processes.

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