Abstract
Electron micrographs of thin sections of Rickettsiella melolonthae in situ show a composite structure like those of bacteria: The protoplasm contains an axial nuclear equivalent. The cell is surrounded by a double membrane. Further studies were made on the development of bipyramidal crystalline inclusions typical for this disease: They originate in albuminoid spheres, and also in vacuoles or vesicles homologous to “NR-bodies”. In these vacuoles, arising from initial bodies, reproduction of the rickettsiae takes place.