Organisation of the tardigrade ventral nervous system. Note the extra-ganglionic, interpedal commissures in front of the second, third and fourth trunk ganglia (arrowheads in A and B ). Combined anti-tyrosinated and anti-acetylated α-tubulin immunolabelling, confocal micrographs (A, B) and transmission electron micrographs (C, D) from Macrobiotus cf. harmsworthi. (A) Detail of the anterior portion of the ventral nervous system. Anterior is up. (B) Detail of the posterior portion of the ventral nervous system. Anterior is up. (C) Oblique sagittal section of a trunk ganglion showing the central fibre mass. Anterior is in the upper left corner. (D) Transverse section of an interpedal commissure. Abbreviations: al, anterior leg nerve; cf, central fibre mass; cn, connective; cx, cortex; ga1–ga4, trunk ganglia 1 to 4; ic, inner connective; nf, nerve fibre; oc, outer connective; pl, posterior leg nerve; pn, peripheral nerve; sc, commissure of the stomodeal complex. Scale bars: 10 μm (A, B), 2 μm (C) and 250 nm (D).