Comparison of the paracoxal ridge (pcr) and metapleural apodeme (pl3a). A. Sceliphron destillatorium, anterolateral view, head left; B. Sphex lucae, anterolateral view, head left; C. Weakly developed structures in Ampulex compressa, lateral view, head left; D. Ampulex compressa, paracoxal ridge, lateral metafurcal arms (fu3a) fused with reduced metapleural apodeme, anterior view. Further abbreviations: pl3lp-t3 – posterolateral metapleuro-metanotal muscle, pl3-tr3 – metapleuro-metatrochanteral muscle, fu3-tr3 – metafurcor-metatrochanteral muscle. Scale bars: 0.4 mm (A–C), 0.3 mm (D).