Fig. 16.

Spatial distribution of the propulsive stresses generated by two terrestrial gastropods while crawling on a gelatin substrate. The data in the left column are from a garden slug and the data in the right column are from a garden snail. (A,B) Contour maps of substrate deformation in the animal's direction of motion. (C,D) Contour maps of horizontal stresses in the direction of motion. These stresses were normalized with the normal stresses caused by the animal's weight (estimated to be spatially uniform and equal to the ratio of the animal weight to the area of the foot). (E,F) Contour maps of horizontal stresses in the direction perpendicular to the motion. (G,H) Brightness images showing the ventral foot of each animal and the marker beads used to measure the propulsive stresses. In both images, the animals were crawling from the left to the right.