amoeba

The amœba and creatures like it live immersed in water; man, at the bottom of an ocean of air.

Both move in their own medium, the amœba creeping with extreme slowness, man moving with a speed incalculably greater.

This latter is to the cells of any tissue, as a muscle, as is the water filled with the food on which an amœba lives.

Although but a single cell, still the amœba appears to be aware of the existence of food when it is near at hand.

When conditions unfavorable for life come, the amœba, like some one-celled plants, encysts itself within a membranous wall.