Transmission electron micrograph (TEM) of a thin section through an endospore of Bacillus subtilis (the hay bacillus"), a species of aerobic, rod- shaped, gram positive bacteria. Endospores (resting cells) are produced in response to nutritional deficiency & adverse conditions, and may later germinate to form a vegetative bacterial cell, if conditions improve. The image shows the thick outer spore coat overlying an layered inner coat. Around the central cytoplasm is a thin membrane that is surrounded by the cortex (lightly stained); central nuclear material appears darkly stained & is typically arranged in filaments. Magnification: X 170,000 at 10x8 size."