. Behavior of the lower organisms. Animal behavior; Invertebrates. REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 135 amined with the microscope in the neighborhood of a window. Soon all the Euglenae are seen swimming toward the window. Now the. Fig. 91. — Diagram of the reaction of Euglena when the light is decreased. The organism is swimming forward at 1; when it reaches 2 it is shaded. It thereupon swerves toward the dorsal side, at the same time continuing to revolve on the long axis, so that its anterior end describes a circle, the Eu- glena occupying successively the positions 2-6. From
. Behavior of the lower organisms. Animal behavior; Invertebrates. REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 135 amined with the microscope in the neighborhood of a window. Soon all the Euglenae are seen swimming toward the window. Now the. Fig. 91. — Diagram of the reaction of Euglena when the light is decreased. The organism is swimming forward at 1; when it reaches 2 it is shaded. It thereupon swerves toward the dorsal side, at the same time continuing to revolve on the long axis, so that its anterior end describes a circle, the Eu- glena occupying successively the positions 2-6. From any of these it may start forward in the directions indicated by the arrows. light is decreased by placing the hand or a screen between them and the window. At once all give the avoiding reaction; that is, they stop or swim backward an instant, then swerve strongly toward the dorsal side, so that the ante- rior end swings about a circle (Fig. 91). If the light is decreased strongly, the anterior end de- scribes a wide circle or may even turn through an angle of 180 degrees, so that the direction of movement is reversed. If only a little of the light is cut off, the anterior end describes only a narrow circle. The organisms soon resume the forward movement, but now the axis of the spiral path coincides with one of the directions indicated by the anterior end in swinging about. 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 Jennings, H. S. (Herbert Spencer), 1868-1947. New York, The Columbia university press, The Macmillan company, agents; [etc. , etc. ]
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