Since the motions of peristaltic organisms are based primarily on changes in the dimensions of the deformable body wall, the scaling of the material properties of the body wall is probably an especially important determinant of the scaling of the kinematics of locomotion. Given the extent of kinematic variation within and among earthworms, the crawling of earthworms of different sizes can be considered to show kinematic similarity when the kinematic variables are normalized by body length. Circumferential and longitudinal body wall strains were generally independent of body mass, while strain rates changed little as a function of body mass. On average, larger worms crawled at a greater absolute speed than smaller worms ( U∝ m b 0.33) and did so by taking slightly longer strides ( l∝ m b 0.41, where l is stride length) than expected by geometric similarity, using slightly lower stride frequencies ( f∝ m b −0.07) and the same duty factor ( df∝ m b −0.03). Preferred crawling speed varied both within and among individuals: earthworms crawled faster primarily by taking longer strides, but also by taking more strides per unit time and by decreasing duty factor. The overall kinematics of peristaltic crawling and the dynamic shape changes of individual earthworm segments were measured for individuals ranging in body mass ( m b) by almost three orders of magnitude (0.012–8.5 g). Whereas the motions of most vertebrates and arthropods are based primarily on the changes in the joint angles between rigid body segments, the motions of soft-bodied organisms with hydrostatic skeletons are based primarily on the changes in dimensions of the deformable body segments themselves. This study examined the relationship between ontogenetic increase in body size and the kinematics of peristaltic locomotion by the earthworm Lumbricus terrestris, a soft-bodied organism supported by a hydrostatic skeleton.
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