Fig. 2. Particle motions. This sequence of consecutive video fields shows the transport of 3 or 4 latex beads from the anterior end of the procorpus to the posterior procorpus or metacorpus. Time in ms is shown in the upper right corner of each image. (A) At time 0 the pharynx is relaxed (lumen closed) and the particles (black arrow), slightly out of focus but detectable by their refractility, are lined up in the anterior procorpus. (B) The contraction has begun (visible as a slight expansion of the procorpus lumen), but the particles have not moved. (C-G) Contraction progresses and the particles are drawn back to the metacorpus. The black arrow indicates the particles. They are not clearly visible in C and E, probably because they are out of focus or moving too rapidly or both; here the black arrow is a guess at their location. Between G and H the corpus muscles partly relaxed and the particles moved forward, three to the posterior procorpus and one to anterior metacorpus. (We do not know whether this fourth particle was at the anterior procorpus at time 0, or out of focus at a more posterior position.) (I) Relaxation is complete. The beads do not move between H and I.

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