Serotonin-like immunoreactivity in median commissures and ventral nerve cords of Metaperipatus blainvillei (Onychophora, Peripatopsidae), micrographs from adult specimens. (A) Fluorescent micrograph of a sagittal vertical vibratome section of the ventrolateral body wall in three leg-bearing segments. Dorsal is to the left, ventral to the right. Dotted lines indicate the dorso-ventral axes of legs, which are sectioned near their bases (lb). The median commissures are arranged regularly throughout the onychophoran body. Nine and ten commissures are seen in two subsequent segments, respectively. Note that two of the commissures are close to each other (small white arrows). Scale bar: 300 μm. (B) Detail of a 5-HT-lir cell body (arrowhead) and its single projection (arrow) situated close to a leg nerve (le). Confocal laser scanning micrograph. Scale bar: 20 μm. (C, D) Whole-mount preparations of ventral nerve cords in ventral view. Two subsequent segments are illustrated in each fluorescent micrograph. Peripheral nerves and several median commissures have been obliterated during preparation. Median is to the right, lateral to the left. The somata of 5-HT-lir neurons (arrowheads) are scattered throughout the nerve cords and do not show any metameric arrangement. Scale bars: 100 μm. (C) Leg-bearing segments 11–12. (D) Leg-bearing segments 17–18. Abbreviations: co, commissures; ep, epidermis; lb, leg basis; le, leg nerves; lm, longitudinal musculature; pe, perikaryal layer; pn, peripheral nerves.