Center: Three different stages throughout encystment of the ciliate Colpoda inflata. Immunocytochemical method using a polyclonal antiserum against isolated cyst wall from this ciliate. Vegetative cell does not react with the antiserum, therefore it shows a red colouring due to contrast dye (red under UV light). Mature resting cyst presents a positive response (yellow-greenish immunofluorescence). A precystic cell (“orange cell” = red + yellow), with an incomplete cyst wall, can be observed between both definitive differentiated stages (vegetative and resting cyst). Courtesy of J. C. Gutiérrez, University Complutense, Madrid, Spain. (Magnification, ca. 1000×) See article by Gutiérrez et al., this issue pp 151–157

Upper left: Transmission electron micrograph of bacteriophage Ø29. Negative staining with uranyl acetate. From Margarita Salas, Center for Molecular Biology "Severo Ochoa", CSIC-UAM, Madrid, Spain. (Magnification, ca. 200,000×)

Upper right: Scanning electron micrograph of square haloarchaea observed in Santa Pola, Alicante, Spain, solar salterns. Micrograph by Silvia González-Acinas and Josefa Antón, University Miguel Hernández, Alicante, Spain. (Magnification, ca. 25,000×)

Lower left: Transmission electron micrograph of Ostreococcus tauri in division. This protist, the smallest known free eukaryotic cell, was identified by C. Courties and M.-J. Chrétiennot-Dinet in Thau Lagoon, France, in 1995. Micrograph by the same authors, from Arago Laboratory, CNRS, Banyuls-sur-Mer, France. Diameter of the dividing cell 1.2 µm (Magnification, ca. 70,000×)

Lower right: Micrograph of several Dematiaceus fungi hyphae from Rio Tinto, Spain. They are acidophilic and resistant to several heavy metals. Micrograph by Ricardo Amils and Anabel López-Archilla, Autonomous University of Madrid, Spain. (Magnification, ca. 400×)