. The evolution of animal intelligence . Animal intelligence; Psychology, Comparative. 34 THE TROPISMS lus. Verworn coined the word thigmotaxis, which is practi- cally synonymous with stereotropism, in order to designate "all those cases of barotaxis in which the phenomena are caused by the more or less strong contact of living substance with solid bodies," the term barotaxis embracing reactions which are "called forth by pressure acting unequally on different sides " of the body. Rheotaxis caused by currents of air or water, geotaxis which according to Verworn is produced
. The evolution of animal intelligence . Animal intelligence; Psychology, Comparative. 34 THE TROPISMS lus. Verworn coined the word thigmotaxis, which is practi- cally synonymous with stereotropism, in order to designate "all those cases of barotaxis in which the phenomena are caused by the more or less strong contact of living substance with solid bodies," the term barotaxis embracing reactions which are "called forth by pressure acting unequally on different sides " of the body. Rheotaxis caused by currents of air or water, geotaxis which according to Verworn is produced by differences in pressure on differ- ent parts and thigmotaxis are all classed by this writer as special cases of barotaxis. Thigmotaxis may be positive or negative, the difference depending in many cases on the strength of the stimulus. This is shown by the reaction of the rhizopod ^%.^ Fig. 3.—Showing the positive reaction of AmcEba to contact with a solid object. (After Jennings.) When quiet this form sends out long and very fine filament- ous pseudopodia. When these are brought in gentle con- tact with another object the protoplasm flows out along the filament and finally draws the whole body toward the object. If the pseudopod is cut or pressed upon by a needle the protoplasm flows centrally and the pseudopod is withdrawn. Amoeba when floating in the water usually sends long pseu- dopods out in various directions. If one of these strikes the bottom it commonly adheres to it; the endoplasm streams into it from the main body and finally the whole AmcEba begins to crawl in the direction of the attached. 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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