Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 PROTECTIVE ACTIVITIES 373 suggests something even milder than a clam. But if you have ever picked up a live jellyfish, you may have thought that a million needles had been shot into your hand. The skin of the jellyfish con- tains a large number of special cells in which there are fine hollow threads that shoot out when the animal is dis- turbed (see Fig. 190). These ' nettling cells ' are found in many spe- cies of coelenterates, such as the hydra, sea anem- one,
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 PROTECTIVE ACTIVITIES 373 suggests something even milder than a clam. But if you have ever picked up a live jellyfish, you may have thought that a million needles had been shot into your hand. The skin of the jellyfish con- tains a large number of special cells in which there are fine hollow threads that shoot out when the animal is dis- turbed (see Fig. 190). These ' nettling cells ' are found in many spe- cies of coelenterates, such as the hydra, sea anem- one, coral polyps, and sea walnuts. But some animals, like the ray, do give their enemies a real electric shock when they are disturbed, and this is no doubt of value in protecting them. The animal that has been shocked quickly lets go and learns to let other shockers alone. Fig. 193. Fighting ants Three forms of the Central American ant Chelio- myrmex nortoiii: a, soldier; b, medium worker c, small worker
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