. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 386 Comparative Animal Physiology Euglena moves directly toward or away from it, depending on the intensity. When the direction of illumination is changed suddenly, the animal re- orients, as shown in Figure 102. This type of orientation is called klinotaxis, a directional orientation made possible by means of regular deviations in movement (pendular or spiral), and involves comparison of intensities at sucessive points in time. The coelenterate Hydra behaves in this way, as do the post-trochophore larva of Aren
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 386 Comparative Animal Physiology Euglena moves directly toward or away from it, depending on the intensity. When the direction of illumination is changed suddenly, the animal re- orients, as shown in Figure 102. This type of orientation is called klinotaxis, a directional orientation made possible by means of regular deviations in movement (pendular or spiral), and involves comparison of intensities at sucessive points in time. The coelenterate Hydra behaves in this way, as do the post-trochophore larva of Arenicola and the tadpole larva of the ascidian Sensory cells Lens Pigment cells. Accessory cells Fig. 103. Diagrammatic representation of photosensitive organs. A, Section through the ocellus of Sarsia. B, Transverse section of the eye of Planaria mactdata. C, Section through eye of Sepia. D, Section through eye of Pecten. Redrawn from Hyman,™ Taliaferro'"^' and Borradaile and Potts.'"'" Amaroucium. Earthworms, under certain conditions, exhibit a pendular movement resulting in orientation, as do the maggot larvae of several species of ; ^^ With the advent of two or more receptors, a peripheral mechanism exists which may permit direct orientation to light. In Planaria maculata, which possesses two cup-eyes, the orientation of the animal is in that direction which results in equal stimulation of both eyes. This type of orientation is called tropotaxis, and involves the comparison of intensities on two receptors simultaneously. Planaria, deprived of their eyes and illuminated, show an. 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 Prosser, C. Ladd (Clifford Ladd), 1907-; Bishop, David W. Philadelphia, Saunders
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