Fully mature Bacillus subtilis spores like this one are ovoid, and swollen with armor, including the thick cortex and multilayered coat. This dense shield protects the cargo within from drying out, or denaturing in heat or acid. (It also makes it hard to make out much internal detail in images.)
Once released, the spore will remain dormant as long as necessary, protected by its carbohydrate and protein armor, waiting for optimal conditions of water, temperature and pH to germinate. The wait can be long, sometimes very, very, very long. In one case, Bacillus subtilis spores were revived from a salt crystal thought to have formed 250 million years ago, about 20 million years before the first dinosaurs appeared.
