Histological studies of the hypertrophied structures of Borneo’s ‘exploding ants’confirm homology with mandibular glands; reservoirs (only) are hypertrophiedas storage structures. The general anatomical organization and ultrastructure ofthe glands is similar to that in other ant species. Development of secretory struc-tures is not unusually great, and secretory cells are apparently confined to thehead. These results suggest gradual production of mandibular gland compoundsand filling of reservoirs and are consistent with known and hypothesized roles ofmandibular glands and their products