. Adventures with animals and plants. Biology. PROBLEM Z What Makes Complex Behavior Possible in Many-celled Aiiimals? Properties of protoplasm. All animals con- sist of protoplasm, and protoplasm has several properties which make it differ- ent from lifeless matter. One of these properties is irritability, the ability to re- spond to stimuli. It is believed that proto- plasm has the property of irritability be- cause it is so complex physically and chemically. Changes in the environment may easily cause changes within it. The physical and chemical changes that take place in the structure of l
. Adventures with animals and plants. Biology. PROBLEM Z What Makes Complex Behavior Possible in Many-celled Aiiimals? Properties of protoplasm. All animals con- sist of protoplasm, and protoplasm has several properties which make it differ- ent from lifeless matter. One of these properties is irritability, the ability to re- spond to stimuli. It is believed that proto- plasm has the property of irritability be- cause it is so complex physically and chemically. Changes in the environment may easily cause changes within it. The physical and chemical changes that take place in the structure of living matter are the direct cause of the responses which the animal makes. When you see streaming in the ameba or lashing of cilia in the paramecium, the protoplasm is exhibiting another of its ipro^&TU&s —C07itractility. The single- celled protozoan can perform reflex acts because it has these two properties, but for you or any other complex animal to perform a reflex act requires more than simple irritability and contractility. In animals that consist of many parts there is a nervous system which is useful in making the many parts of the animal work together. Reflex acts, as well as all learned acts, in complex animals are pos- sible because of the nervous system. Let us study this important system. The nervous system. You know what happens when someone accidentally puts his outstretched hand into a flame. He pulls his hand out of the flame. But he also feels pain and probably has a sudden fright together with a rapid heart beat, a catching of the breath, and perhaps a tight feeling about the abdomen. How does it happen that so many organs re- spond to the one stimulus? Fig. 253 Vor- ticella, a tiny one-celled ani- mal, is attached by a contractile stalk. One Vor- ticella has just been touched by a glass rod. How did it re- spond? What two properties of its proto- plasm 7nalie this possible?. Contractile fibrils in stalk. Please note that these images are extracted
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