Figure 1.

Wild-type C. elegans interacts with the bottom surface. (a) The experimental set-up to image C. elegans motions in the vertical plane. (b) Video frames showing a C. elegans propelling along a surface: side view ((i), electronic supplementary material, video S2) and rear view ((ii), electronic supplementary material, video S3) while colliding with the bottom surface. The dots denote the position of the animal's head. (c) The experimental set-up used to concurrently image the motion of animals in a capped conduit in two orthogonal planes. (d) Top view (i) and side view (ii) of an animal swimming in a conduit while interacting with the floor and ceiling of the conduit (electronic supplementary material, video S4). We used a higher magnification and artificial colour in the side view images to enhance visibility. (Online version in colour.)