Fig. 2. Antennal flagellum of Libellula depressa under TEM; (a–d) coeloconic sensillum; (e–h) type-1 deeply sunken sensillum; (a) longitudinal section of the coeloconic sensillum showing the dendrites (D) entering the peg; the dendrite sheath (DS) becomes very thin at the base of the peg (arrow head). Note the pore-like structures on the peg cuticle (arrows). Scale bar ¼ 2 mm; (b) detail of Fig. 2a showing the actual pores (P) at the base of the wide pore-like structures. At this level the dendrite sheath leaves only some traces (double arrow). An asterisk indicates the narrow, medium electron-dense space between the cuticle (C) and the dendrites (D). Scale bar ¼ 0.5 mm; (c) cross section of the coeloconic sensillum at the level of the peg. Note the dendrites (D) without dendrite sheath and the pore-like structures (arrows) on the cuticle (C). Scale bar ¼ 0.5 mm; (d) cross section of the coeloconic sensillum at the level of the outer dendritic (OD) segments enveloped by the dendrite sheath (DS) secreted by the thecogen (Th) cell. Scale bar ¼ 2 mm; (e) longitudinal section of the peg of a type-1 sensillum showing the dendrites (D) entering the stylus, which are enveloped by a thick dendrite sheath (DS). In the sensory cone, the cuticle (C) is interrupted and the dendrites are in contact with a cap-like structure (Ca) covered by cuticular fingers (CF). Note in cross section the outer dendritic (OD) segments and the highly developed trichogen (Tr) and tormogen (To) cell, with long microvilli (MV) and electron-lucid vesicles (V). Scale bar ¼ 2 mm; (f) cross section showing three sensory neuron somata of the four neurons (N) innervating the sensillum. Scale bar ¼ 5 mm;(g) cross section at the level of the inner dendritic (ID) segments. Scale bar ¼ 1 mm; (h) cross section at the level of the ciliary constrictions (CC). Note the thecogen (Th) cell secreting the dendrite sheath (DS) and containing a scolopale-like structure (Sc). Scale bar ¼ 1 mm. AC, accessory cell; M, mitochondria; Nu, nucleus of the trichogen cell