Walking in a millipede
(Arthropoda, Myriapoda)

 A      B 

CONTROLLING THE ANIMATION:
Wait for the animation to load completely and play through once. To stop the animation, click on the "pause" button. To see the frame that precedes the paused frame, press the "previous" button. To see the frame that follows the paused frame, click on the "next" button. To resume the animation, click on the "play" button.

PROCEDURE:
1) Lay a small clear transparency sheet over the animation (Fig. A). Use two small pieces of paper tape to secure corners of the transparency sheet to the monitor screen. Use a marking pen to make a series of dots on the sheet that track the frame-by-frame position (starting at time = 0) of the millipede's head end as it walks. [NOTE: Each frame of motion represents 1/30th second (= 0.033 sec) of elapsed time. Thus frames are numbered 0.000, 0.033, 0.067, 0.100 sec, etc.]  Make sure the correct elapsed time is recorded for each point of progress and make sure the distance scale is carefully recorded on the transparency  sheet.
2) Remove the transparency sheet and lay it on a piece of white paper. Then, estimate the forward velocity of walking, as determined by computing the millipede's forward progress during a 0.500 sec interval (= 1/2 sec). Express units in mm/sec.
3) Pause the image and look closely at the position and angle of the millipede's legs in different locations along the body. In the animation, the view is from above, so the short legs of the millipede are seen on both sides of the body. In Fig. B, note at some locations that the tips of adjacent legs angle toward one another and thus converge while at other locations the legs angle away from one another and thus diverge. At locations where legs diverge, the legs are actually in contact with the ground and are functioning to power the body in a forward direction. This phase of locomotion is called the power stroke. At locations where legs converge, the legs are being lifted off the ground and are swinging back to a forward-pointing position. This phase of locomotion is referred to as the recovery stroke.  Use a paused frame to make a tracing of the millipede, carefully noting leg positions. Label locations where legs are in the power stroke and recovery stroke phases. 

4) Now, advance the animation for 10 consecutive frames carefully recording the change in location (relative to the head end) of one specific area where the legs converge in a recovery stroke. You should observe that, with each frame, this recovery stroke area moves in a wave-like fashion relative to the head end.  In which direction does this wave move - forward or rearward?  
5) Note whether the left and right legs within a given segment of the millipede are in the same phase, or in an opposite phase, of walking. Compare this left-right phase relationship with that seen in the house centipede, Scutigera.

Click here to see non-interactive GIF animation 
Software for controlling interactive animations was developed by TOM DREWES