Fig. 4. Results from experiments involving (A) covering the burrow, (B) radial translational displacement and (C) tangential translational displacement. (A) Data from three different crabs were overlaid and aligned with one burrow entrance (filled gray circle); lines represent the center of each crab's carapace. (B,C) Position of muddy, mobile acetate sheet before (solid rectangles) and after (broken rectangles) displacement, with the sheets' motion vectors indicated by gray arrows. Fictive burrow entrances (large open circles) are found by adding this motion vector to the true burrow entrance (gray filled circles). Lines represent the center of each crab's carapace, the period during which the crabs were on a moving substrate being indicated by connected black dots. In these figures, `start' indicates the beginning of the digitized track; in A, only the homeward part of the crabs' tracks were digitized, while in B and C both outward and homeward journeys were digitized. Scale bar in C also applies to B.