. The animans and man; an elementary textbook of zoology and human physiology. 68 THE ANIMALS AND MAN. FIG. 26. Diagrams showing fundamental structure of types of severalanimal phyla: 1, sea-anemone; 2, starfish; 3, worm; 4, centiped;5, clam; 6, honeybee; 7, salamander. In each figure the centralnervous system is indicated by the black lines. (After Haeckel.) ANIMAL PHYSIOLOGY 69 Light, for example, has always a definite influence on certainsimple animals compelling them to move in certain waysand to continue moving until they have arranged theirbodies in a fixed position with regard to the di
. The animans and man; an elementary textbook of zoology and human physiology. 68 THE ANIMALS AND MAN. FIG. 26. Diagrams showing fundamental structure of types of severalanimal phyla: 1, sea-anemone; 2, starfish; 3, worm; 4, centiped;5, clam; 6, honeybee; 7, salamander. In each figure the centralnervous system is indicated by the black lines. (After Haeckel.) ANIMAL PHYSIOLOGY 69 Light, for example, has always a definite influence on certainsimple animals compelling them to move in certain waysand to continue moving until they have arranged theirbodies in a fixed position with regard to the direction of thelight rays. Certain chemical substances, as well as gravita-tion, magnetism and other external agencies exert similarlydefinite influences. These externally controlled movementsare called tropisms. Various other animal motions are ofsuch a definite character, always recurring in exactly thesame way under the same conditions of stimulation, thatthey are called reflexes; and these also go to show, as do thetropisms, that much of the behavior of the simpler animals,and even more or less
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