All ants studied so far have a convoluted gland portion as part of their venom gland. The venom glands of the amblyoponine genera Amblyopone, Mystrium, Onychomyrmex and Prionopelta, however, are characterized by the absence of a convoluted gland, which makes this ponerine tribe exceptional among ants. The venom gland of Amblyoponini is similar to that of mutillid wasps, which supports a possible tiphiid ancestral form. Ultrastructurally, the cells of the free tubules do not differ from those of most other stinging ants. A separate series of secretory cells, each with its own end apparatus, lines part of the venom reservoir. These few secretory cells near the orifice of the glandular tubule into the reservoir show an end apparatus with wide extracellular spaces and are similar to those lining the venom reservoir in honeybees. Several muscles run parallel with the longitudinal axis of the reservoir, which results in the curved appearance of replenished reservoirs when these muscles contract.