Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Confocal image of a Drosophila stage 15 embryo showing the developing trachea and tracheal fusion cells. The fusion cells, marked by anti-Dysfusion staining (green), lie at the tips of developing tracheal branches and mediate their fusion. Tracheal cells are stained with anti-Trachealess (red). (See related article on p. 5625.)