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Silver lactate autometallography in immunogold silver staining (IGSS) usually requires development in darkness to avoid excessive background staining. Our alternative method of silver enhancement of IGSS on paraffin sections from Bouin's or formalin fixed pancreas uses silver acetate in combination with hydroquinone in low pH buffer. The modification was tested with a range of antibodies in normal and diseased tissues (all routinely fixed and paraffin embedded), in acetone postfixed cryostat sections, and in semithin sections of glutaraldehyde fixed and resin embedded tissues. Silver acetate autometallography was also tested in various systems for the visualization of tissue metals like sulfides and selenides of mercury and zinc, silver, and gold. Comparisons between sections exposed to silver lactate and the silver acetate developer showed no significant difference in the number of structures stained. The degree of background staining was often lower when silver acetate was to used as the ion donor, especially with IGSS. The advantage the technique described here is that the development process can be controlled, using normal bright field light microscopy. (The J Hktotechnol 1 1: 213, 1988.)

Oxytricha granulifera sp.n. differs from other members of the genus by its subpellicular granules and the strongly shortened dorsal kinety 4. The overall pattern of the morphogenetic events is similar to that known from other Oxytrichidae. However, the oral primordium evolves de novo between the left marginal cirral row and the postoral cirri. The six anlagen of the frontoventral cirri are of different origin. Two anlagen of the proter evolve from parental frontal cirri, two from the opisthe, and one includes basal bodies of the proter and opisthe. Two anlagen of the opisthe evolve from the oral primordium, and three primordia originate from the postoral cirri. Frontal cirrus 1 evolves from the paroral membrane in the proter, and from the oral primordium and the anlagen of the frontoventral cirri in the opisthe. The genus Oxytricha can be subdivided into several groups with regard to the origin of its oral primordium and the development of the frontoventral cirri. The morphogenesis of the dorsal kineties in the Hypotrichida is reviewed. Seven different modes of origin are distinguished. We conclude that morphogenetic features cannot be used in the classification of the Hypotrichida at the generic level, because we have too little information to decide whether special morphogenetic features are important at the generic or species level.

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