THE CLYPEUS AND THE EPISTOMAL SUTURE IN HYMENOPTERA

Abstract

The frontoclypeal suture in the Hymenoptera does not arch upwards into the frontal region but retains its primitive position at the horizontal level of the mouth, the clypeus remaining preoral in position. The genae and postgenae have continued or resumed their ventral growth, the inner margins of the genae have fused with the previously free lateral edges of the clypeus, and a pair of clypeogenal sutures, continuous with the frontogenal, have formed along the lines of fusion. The clypeogenal sutures form the vertical or oblique elements of the U-shaped epistomal suture, while the frontoclypeal suture forms its horizontal component. The anterior tentorial pits, within the bases of the frontogenal sutures, lie at the junction of the frontoclypeal with the clypeogenal sutures. These changes in the structure of the face have caused a ventral shifting of the mandibular articulations.