Phototaxis of gef mutant slugs. (a) Traces of slug trails from slugs migrating towards a light source to the right of the figure. Slugs migrated on charcoal agar plates; trails were transferred to white filters and stained with Coomassie blue. (b) Accuracy of slug phototaxis at different starting cell densities. Different quantities of cells were deposited on a charcoal agarose plate and allowed to move for 48 h. Trails were visualized as above, and phototactic efficiency was measured as described in Materials and methods. The inset shows data for gefE and gefL mutants replotted with different axes to reveal significant, if diminished, phototaxis in each case. Other mutants behaved apparently normally (data not shown). (c) Dependence of slug thermotaxis on temperature. Cells were plated and thermotaxis measured as described in Materials and methods. Other mutants behaved apparently normally (data not shown).