RESUMEN
A simple method is presented by which synaptonemal complexes (SCs) can be visualized under bright field microscopy. Staining was accomplished with a silver nitrate solution adjusted to pH 3-3.5 with formic acid, after an acidic fixation. This method is suitable for the demonstration of SCs, centromeres and NOR regions in both mammalian (Rattus norvegicus, 'Wistar') and orthopteran spermatocytes (Steropleurus martorelli complex). Results suggest that pretreatment with solutions of alkaline pH are not needed for demonstrating SCs, and that the silver impregnation may also operate when the proteinaceous lateral elements of the SC are subjected to low pH conditions. Differential staining of the X chromosome during meiosis in Orthoptera, and a core-like structure in the chromosomes during the more condensed stages of meiosis and mitosis can also be shown.