LOCOMOTION OF EARTHWORM

Movement in earthworm involves the musculature of  body wall and setae. According to the studies of Gray and Lissman (1938) ,  the worms body undergoes extension, anchoring and contraction during the course of its progression.  A wave of contraction, affecting circular muscles, begins at the body to become thinner and longer.  This is followed by another wave of contraction affecting longitudinal muscles causing thickening and shortening of body. This is again  followed by the wave of thinning and the process is repeated alternately. Each wave  of   circular contraction causes the segments affected to move forward. But the segments in a  state of longitudinal contraction do not move as  they are  anchored to the ground by the protruded setae. Setae always protrude  during longitudinal contraction and retract during circular contraction. It has been calculated that, by its method,  the earthworm travels  a distance of about 25 cm in one minute. 

         when the direction of waves is reversed, the worm crawls backwards.

During locomotion , coelomic fluid serves as a kind of hydraulic skeleton. When compressed due to contraction of circular muscles,  it provides  stiffness to body   and    aids  in   relaxation   of   longitudinal   muscules.