. Animal biology. Zoology; Biology. Fig. 18.—Sketch showing a long, rectangular glass aquarium partly covered by an opaque hood, and containing three species of organisms responding differently to light. The direction of the light is shown by the arrows and the positions assumed by the animals at + (positive), - (negative), and ± (gradient). of stimulation or to avoid it, it is termed a negative response. The mini- mum strength of the stimulus which is necessary to produce an effect is termed the threshold of stimulation. Some animals do not seem to respond positively either to the strength of
. Animal biology. Zoology; Biology. Fig. 18.—Sketch showing a long, rectangular glass aquarium partly covered by an opaque hood, and containing three species of organisms responding differently to light. The direction of the light is shown by the arrows and the positions assumed by the animals at + (positive), - (negative), and ± (gradient). of stimulation or to avoid it, it is termed a negative response. The mini- mum strength of the stimulus which is necessary to produce an effect is termed the threshold of stimulation. Some animals do not seem to respond positively either to the strength of the stimulus immediately above the threshold or to a maximum strength of the stimulus but do seem to be attracted to a position in which they receive the stimulus in a degree intermediate between the maximum and minimum. In this case they are said to exhibit a response to a gradient of the stimulus, corresponding to an intermediate strength expressed in degrees of temperature, intensity of light, or concentration of chemical solution (Fig. 18). 87. Conductivity.—Though the stimulus may be received at a particu- lar point on the animal, the effect is not limited to that point but is con- ducted more or less throughout its body. This power of living matter to transmit the effect of the stimulus is termed conductivity. Irritability, or reactiveness, which is the power to respond to stimuli, as well as con-. 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 Wolcott, Robert Henry, 1868-1934; University of Nebraska (Lincoln campus). Dept. of Zoology. New York ; London : McGraw-Hill Book Company, Inc.
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