The property of some Hemiptera, more especially the Pentatomidæ and Cimicidæ, of emitting an offensive odor when disturbed or injured has been known for many years. The first record of the source of the secretion which produces this odor showed it to be a gland in the ventral part of the metathorax opening to the exterior by ducts on either side in front of the hind coxæ. Later it was found that similar glands in some of the dorsal segments of the abdomen of the nymphs had the same property but upon molting to the adult stage these glands disappeared and were apparently replaced by those in the metathorax without any change in function.