Fig. 5
Internal ultrastructure of the scape organ based on TEM analysis: Overview and details of median and proximal components with focus on receptor cells with short outer dendritic segments and scolopidial elements. A Cross-section of inner sensillum lymph space housing the four long plus two short outer dendritic segments. The short outer dendritic segments are cut at a level where they just transform into tubular bodies. B Cross-section slightly proximal of (A), illustrating all six outer dendritic segments with similar diameters. Note the scolopale-like structure in the first sheath cell. C Slightly oblique overview of the median region of the receptor and accompanying sheath cell cluster (asterisks). Flattened, strongly stretched epidermal cells are cut at their nuclear level in between and outside receptor and sheath cell clusters, spread by an enormously expanded extracellular space. D Insertion zone of outer dendritic segments showing ciliary structures. Oblique-transverse section of the widened inner sensillum lymph space containing five profiles of outer dendritic segments. A further profile is cut at the transition zone of the outer and inner dendritic segment coinciding with the presence of a basal body. E Approximately the same region as shown in (D), but from a transverse perspective. All three inner dendritic segments are present. Two of them are cut at various levels of the basal body region. The mid profile displays two basal bodies underlining the biciliated nature of receptor cells. F–H Three cross sections taken from the proximal region of the receptor cell apparatus cut at the level of (F) dendritic inner segments, (G) the somata level, and (H) the axonic level. ax, receptor cell axon; bb, basal body/bodies; css, cellular profile of cone-shaped sensillum; dbb, distal basal body; ds, dendritic sheath; epc, interstitial epidermal cell; esp, extracellular space; gc, glial cell; ids, inner dendritic segment; isl, inner sensillum lymph space; mi, mitochondria; mv, microvilli; ntb, neurotubules; ods, outer dendritic segment(s); pbb, proximal basal body; rc, receptor cell; rER, rough endoplasmic reticulum; rf, ciliary root fibers; sco, scolopale-like structure; sej, septate junction; shc1, first sheath cell (scolopale cell); trz, transition zone (of the basal body)