LEECH PHOTORECEPTOR CELL - ULTRASTRUCTURE OF CLEFTS CONNECTING PHAOSOME WITH EXTRACELLULAR SPACE DEMONSTRATED BY LANTHANUM DEPOSITION

When the extracellular space in eyes of Hirudo medicinalis was traced by means of lanthanum deposition, clefts were found which extend into receptor cells connecting the phaosome vacuoles with the extracellular space. The membrane of the phaosome, which bears the photoreceptor microvilli, is continuous with the external membrane of the receptor cell. Thus mechanisms by which the initial events of photoreception bring about electrical events at the cell surface need not differ from those being considered for other photoreceptor cells. Intracleft structures were revealed in negative constrast by the lanthanum deposits. Bridges join the opposed membranes on either side of a cleft. Isolated isodiametric profiles (120 A in diameter), and zig-zag linear structures, that are perhaps linear arrays of the isodiametric structures, were revealed in tangential sections of lanthanum filled clefts. © 1969 Springer-Verlag.