In 1833 Leon Dufour described and figured in his "Recherches sur les Hemipteres,''* under the non-committal name of "cordons valvuleux," some curious appendages of the alimentary canal in Scutelleridae, Pentatomidae, and certain Coreidae, misinterpreting their structure, however, and expressing no opinion as to their function, which, in fact, he called a mystery .f These organs had been previously distinguished by Ramdohr (1811), and they have since been several times referred to by entomologists as glands or follicles secreting a digestive fluid, presumably pancreatic. My own entomological studies did not make me particularly acquainted with structures of this class until 1888, in the autumn of which year, while studying the contagious diseases of the chinch bug {Blissus leucopterus) I made some dissections of that insect, isolating the alimentary canal and searching different parts of it for the source of a bacterial infection discovered in the fluids of chinch bugs when crushed under the microscope. This bacterial development I thus traced to certain coecal appendages of the small intestines so unlike the 'cordons valvuleux' of Dufour's descriptions, that it did not for a time occur to me to connect the two; but in the course of some general dissections of Hemiptera made at my office this summer by my assistant,
Mr. John Marten, and myself, it became evident that these dissimilar organs could be connected by intermediate gradations, that they had substantially the same anatomical relations and histological structure,
and that all were alike, wherever they occurred, in the highly remarkable fact that they were invariably loaded with myriads of bacteria, differing in genus and species in the different insects, but always confined to these
organs.* We further observed that in Coreidae and Lygseidse these coecal structures might be present in one genus and absent in another of the same family, only the higher Hemiptera (Pentatomidae, Scutelleridae, Corimelaenidae, etc.) invariably possessing them, and
the lower Hemiptera invariably wanting them. In case they were absent, their bacterial relationship was never assumed, in whole or in part, by any other organ. The occurrence of "masses of motile vibrio-like objects" in these glands in a Pentatoma was noticed by Leydig in 1857, but I have found no other mention of the matter than that on page 337 of his Lehrbuch der Histologie.Ope
