p The form in which material entities reproduce the peculiarities of bodies affecting them depends on the nature of tiipsp pntitips. Qualitatively dif-

p ferent material entities therefore reflect one and the same action in different ways. The difference in the forms of reflection is especially evident when matter passes from one qualitative stage to another.

p In inanimate nature, reflection constitutes a corresponding change of the physical properties or chemical reactions reproducing in one way or another the peculiarities of the interacting bodies or phenomena. In the simplest animal or vegetable organisms, reflection is manifested in the form of irritability, which is a response to an outside action, the response having a certain direction of actions,  [119•1  a certain selectivity. For example, a plant reacts to the action of sunlight by changing the position of its leaves-it turns them in such a way that they become perpendicular to the falling rays. This position helps the plant to absorb a greater quantity of solar energy which is essential for its functioning and development.

p The emergence of more complex and developed living organisms, particularly those with a nervous system, has made reflection more complex. Now it assumes the form of excitability, a distinctive feature of which is that a special organ—the 120 nervous system—begins to perform a reflecting function. This system controls the interaction of the organism with the outside world. Its separate tissues or cells perceive outside actions, while others transmit the resultant irritation to the cor responding parts of the organism, thereby ensuring the performance of the necessary responsive action.

p Originally, the nervous system existed in the form of nerve tissues and cells scattered all over the animal’s body. Later it underwent substantial changes during the organism’s subsequent development. Separate nerve cells inosculated and formed nerve ganglia connected by the nerve trunk. Then nerve ganglia combined, thus causing the development of special centres-the brain and spinal cord—and forming the central nervous system. The latter’s appearance caused substantial changes in the reflecting activity of an organism. Previously, living organisms reacted only to irritants connected with their vital activities, whereas now that the central nervous system has evolved, they begin to react to irritants which of themselves have no importance for the organism, but are linked to phenomena vital for it. In other words, the interconnection of an organism with the surrounding world was previously maintained on the basis of unconditioned reflexes, whereas now the latter have been supplemented with conditioned reflexes. These allow the organism to reflect connections between various phenomena that are not vital for it and those that are. Thanks to this, animals have become able to react 121 sensitively to environmental changes and to adapt themselves accordingly.

The form of reflecting reality through conditioned reflexes differs greatly from the preceding forms, such as irritability and excitability. The latter were biological forms of reflection, while conditioned reflexes are a form of psychological reflection of reality.