One of the cell types occurring in the connective tissue of gastropods and bivalves is thepore cell. Cells of this type have a characteristic morphology in that their plasmamembrane has many invaginations bridged by cytoplasmic tongues. In the well developed granular endoplasmic reticulum and in these invaginations fine granular material, sometimes arranged in crystalline patterns, is present. InLymnaea stagnalis this material has been identified as haemocyanin on a morphological basis. Histochemical and ultrastructural results on pore cells of 2 snail species(Biomphalaria glabrata, Planorbarius corneus) having haemoglobin in their blood indicate that the pore cells in these species synthesize haemoglobin. Possible other functions of pore cells are briefly discussed.