Mushroom bodies in beetles of the families Histeridae, Staphylinidae, Cantharidae, Trogossitidae, Peltidae, Cleridae, Malachiidae, and Coccinellidae are shown to be rather poorly developed. The calyx region of the mushroom bodies in these beetles never forms two separate cups, and the peduncular apparatus includes a unified shaft almost over its entire length. Only the pedunculus contains two separate shafts in a few cases. Two proliferative centers consisting of one to three neuroblasts are often found in each Kenyon cell group. The shift from carnivorous to feeding on pollen or leaves, which has taken place in some taxa, does not visibly affect the degree of mushroom body development.