The study of Cl. septicum by means of electron microscopy revealed that these organisms had peritrichously located flagella and the five-layer cell wall. The formation of small oval spores was observed by the end of the first day. The first sign of sporulation was the appearance of the prespore membrane followed by the formation of the prespore; the formation of the spore coat and the spore cortex began simultaneously at stage IV. The spore coat appeared first as short osmiphil scales. They were located at a certain distance from the outer prespore membrane and had a three-layer structure. Later these scales grew longer and merged, forming an electron-dense layer around the spore. The exosporium had a multilayer structure. Cl. septicum spores had characteristic spiniform processes on the exosporium surface.