Figure 2

Histological organization and ultrastructure of the palpal bulbus of Philodromus cespitum. (A) Virtual medio-longitudinal section of bulbus based on 3D X-ray microscopy. Neural and sensory tissues are highlighted in yellow: bulbus nerve passing through the cymbium and entering the bulbus. Section planes illustrated in (B,C) and (D) are indicated by black lines. Note that further branches of the pedipalp nerve projecting through the cymbium are not highlighted. (B–D): Light microscopy; (B –D): TEM. (B’–D’): Sequence of semithin cross-sections of the bulbus showing the ___location and extension of aggregated internalized sensilla and associated nerve: (B) exhibits cross-profile of the bulbus nerve, (C) shows the deeply sunk cluster of somata of sensillar receptor cells, while (D) highlights distal (dendritic) components of the sensilla. (B’ –D’): Ultrastructural insights from cross-cut bulbus nerve (B’) showing neurite bundles in four distinctive compartments as separated by glial cell sheaths. (C’): Cell cluster adjoining fundus gland, it contains somata of sensillar receptor cells enwrapped and invaded by glial cells. (D’): Proximal aspect of dendritic system of sensilla, pairs or (occasionally) clusters of more than ten dendritic inner segments are visible surrounded by sheath cell somata. BH – basal haematodocha, BN – bulbus nerve, BV – blood vessel, Cy – cymbium, DIS – dendritic inner segment, Em – embolus, EGC – embolus gland cells, FG – fundus gland, FGL – fundus gland lumen, GC – glia cell, HeS – hemolymph space, InS – internalized sensilla, S – spermophor, SC – somata cluster, SF – seminal fluid, SG – spermophor gland, ShC – sheath cell, NeB – neurite bundle, So(RC) – soma of receptive cell.