These are images of a fixed C. elegans animal that has been labeled to illuminate muscle and neuronal cells. The upper left panel shows the bright field image of this animal, with the anterior oriented to the left. The upper right panel is an epifluorescence image in which the muscle cells are highlighted with a red flourochrome-labeled muscle probe, phallacidin. In the lower left panel is a fused epifluorescence image in which most of the C. elegans neurons are also labeled in green by their endogenous expression of an engineered Green Fluorescent Protein transgene (unc-119/GFP, courtesy of M. Maduro). Note the nerve ring in the anterior and the ventral nerve cord running the length of the animal. In the lower right panel, all C. elegans cell nuclei are also stained with the DNA-specific fluorescent dye DAPI.