. The evolution of animal intelligence . Animal intelligence; Psychology, Comparative. 52 THE TROPISMS tion and the nature of their locomotor organs. There are comparatively few cases in which light orients an animal by causing directly a greater contraction of the muscles of the side most affected. The observations of Mast on the planulae of Eudendrium indicate that these forms may be oriented in this way. Eudendrium planulae are cone- shaped organisms with the wide end in front, and having the body covered by cilia by means of which they swin through the water. According to Mast, "if th
. The evolution of animal intelligence . Animal intelligence; Psychology, Comparative. 52 THE TROPISMS tion and the nature of their locomotor organs. There are comparatively few cases in which light orients an animal by causing directly a greater contraction of the muscles of the side most affected. The observations of Mast on the planulae of Eudendrium indicate that these forms may be oriented in this way. Eudendrium planulae are cone- shaped organisms with the wide end in front, and having the body covered by cilia by means of which they swin through the water. According to Mast, "if the ray direc- tion is but slightly changed after the planulse are oriented. FiQ. 5.—^The water scorpion Ranatra, showing the different attitudes assumed according as the light falls upon it from in front or from behind. The arrows indicate the direction of the rays. they do not turn directly toward the source of light in its new position, but merely swing the anterior end a little far- ther toward it each time. In the meantime the body grad- ually turns so as to become oriented again. If however the direction of the rays is changed to such an extent that the sides of the organism become fully exposed, they with very few exceptions appear to turn toward the light at once. In this process they swing the anterior end laterally until it nearly if not quite faces the source of ; The larvae of Arenicola according to Lillie orient them-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Holmes, Samuel J. (Samuel Jackson), 1868-1964. New York : Holt
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