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FIGURE 6.1 Female Ascaris suum in locomotory posture. Position of head ganglia and
tail ganglia are circled. The extent of the pharynx is indicated by gray shading. Panels to
right show neuronal cell bodies (filled profiles; their relative size is to scale) in anterior
ganglia and in tail ganglia. Dotted area in the tail indicates the rectum. Numbers of neurons
in head ganglia, pharynx, lateral lines, ventral nerve chord, and tail are indicated, for
a grand total of 298 neurons. The total for Caenorhabditis elegans is 302 4 . NR, nerve ring; VG,
ventral ganglion; LG, lateral ganglion; DG, dorsal ganglion; LL, lateral line; VC, ventral
nerve cord; DC, dorsal nerve cord: RVG, retrovesicular ganglion.
respectively, and produce the mostly dorsoventral muscle contractions of
the propagating body waveform during locomotion. The major nerve
cords also include interneurons, just two in the DC, and about 30 in the
ventral cord (depending on the position along the animal). There are also
four sublateral nerve cords (two subdorsal and two subventral) that are
close to the lateral lines. They give rise to dual innervation of anterior
muscles, 34 and are believed to generate three-dimensional movement
of the anterior part of the worm. The sublateral cords gradually taper
in diameter and eventually terminate near the vulva; the density of
neuromuscular connections similarly declines, corresponding with the
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