An Introduction to the Invertebrates, Second Edition - tiera.ru

52 ON BEING A WORMGraphical representation of lattice action considers the wormas a cylinder. Thenvolume ¼ length cross-sectional ðTSÞ areaand this area is proportional to the square of the diameter. Sincethe fibre of which the lattice is made cannot change in length, thevolume and the lattice angle will be related as shown in Figure 5.1e.Since a worm does not change in volume but in length, it mustbe represented on this graph by a horizontal line such as AB. A andB represent extremes of the lattice system: the worm cannot beFig. 5.1 Worm locomotion.(a) Peristalsis: successive stagesin the forward movement of anearthworm. (b) Waves of musclecontraction passing from theanterior to the posterior end ofan undulating worm: forcesgenerated (above) and resultinglocomotion (below).