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The amoeba, sometimes called the simplest of the protozoa, can be collected from the under surface of water lilies and the stems of water plants. This unicellular animal appears as a gray blob of jelly, somewhat granular, flowing along in no definite shape but extending what resemble "feet" of protoplasm. It has no mouth, but engulfs food as it flows over it.
These food particles can be found within the cell in a drop of water picked up by the amoeba when engulfing the food. The food can be seen as a darker mass within the cell, undergoing digestion. Waste products are simply left behind as the amoeba continues to flow along.
The amoeba lives in salt as well as fresh water, and even in damp soil. Should its surroundings become difficult, that is, should a pond dry up, the amoeba has the ability to encyst itself by secreting a shell for protection. Amoebas are also found internally in higher forms of animal life, where they can be either harmful or not.
Some species are responsible for disease, such as the dysentery amoeba in man. One other species, the mouth amoeba, is found in human teeth and gums, where it feeds on bacteria and loose cells, but has not been proven to be particularly harmful.
Some species pick up grains of sand and cement them together to form a house into which they retreat when disturbed.