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In all waters, daphnia abound. They are crustaceans about 2 ml long, with one eye that turns in all directions. Antennae enable daphnia to move: in a close up magnified 150,000 times, we see the muscles of the antennae pulse. We see the eye, the nerve mass, blood globules, and the heart, beating several times per second. The intestine forms a long line. All are females; eggs develop above the intestine. New generations come rapidly. Inside each daphnia are tiny infusoria; we watch them clean the intestine of a dead daphnia. An enemy, the hydra, approaches. A daphnia dies, but many remain.
