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Didinium attacks Paramecium. Coloured scanning electron micrograph (SEM) showing a one-celled Didinium (brown) in the process of attacking a one-celled Paramecium sp. (blue). These animals are ciliate protozoans, both bearing cilia. The barrel-shaped Didinium has two girdles of loco- motory cilia, and a prominent snout which is used as a probing and seizing organ during feeding. The Paramecium has cilia across its body used for movement. The Didinium has manoeuvred the Para- mecium, almost twice its own size, into an easier position for ingestion. The Didinium's snout and gullet are expanding in preparation for the meal. Magnification: x600 at 6x7cm size. (KEYSTONE/SCIENCE PHOTO LIBRARY/EYE OF SCIENCE)