The role of the "third eye" in reptilian behavior. American Museum novitates ; no. 1870

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New York, N.Y. : American Museum of Natural History
"The function of the parietal eye in four species of western North American lizards was investigated by surgical removal of the 'eye' (parietalectomy) and by covering the 'eye' with aluminum foil. The species studied were Sceloporus occidentalis, S. undulatus, Uta stansburiana, and Uma inornata; the first two species were investigated most intensively. A population of Sceloporus occidentalis in Berkeley Hills, California, was studied from September, 1955, to June, 1957. Marked parietalectomized and sham-operated individuals were returned to the field to original points of capture, and their subsequent behavior was observed. The two surgical types were always introduced in equal numbers. Other lizards were studied in photothermal gradients in the laboratory. The following results were obtained: 1. Individuals of all four species increased their exposure to sunlight (or artificial light in the laboratory) following removal of the parietal eye. There was prolongation of the time spent exposed on the surface of the ground and greater use of high-intensity illumination. 2. Although these lizards are heliotherms, depending directly on the sun for elevation of their body temperature to desired levels, no differences were found between the parietalectomized and control lizards in body temperatures recorded during the period of surface activity. Both in the field and laboratory, however, the parietalectomized lizards extended the length of time spent at the thermal levels of 'normal activity.' 3. The increased exposure to sunlight following parietalectomy is accompanied by increased locomotory activity, as judged by the restive behavior of captives and the shifts in position of surgically treated lizards released in the field. The parietalectomized animals average three times greater displacement from previously determined home ranges than the sham-operated animals. 4. The parietalectomized lizards were less inclined to retreat upon the approach of the observer than were the sham-operated ones. The pronounced heliothermism perhaps works antagonistically to the normal retreat reaction. 5. The thyroid gland of parietalectomized lizards tended to show hypertrophy and loss of colloid, which suggests that there is a relationship between thyroid and the behavioral changes observed. 6. That sunlight is the stimulus to the parietal eye seems indicated by the increased heliothermism that occurred following the use of aluminum foil shields over the 'eye.' In experiments with foil, the parietal eye was left intact. 7. Parietalectomized lizards deprived of food appeared to be less viable than sham-operated lizards. Increased metabolism probably resulted in more rapid exhaustion of their energy reserves. Additional work is, however, required before this point can be fully documented. 8. Microsections of the parietal eye of Sceloporus failed to reveal any nerve connection between the 'eye' and the brain. The retina of the 'eye' appears to be secretory, and its activity probably fluctuates with the intensity of solar radiation to which the eye is exposed. It may be concluded that the parietal eye in the diurnal lizards studied functions in helping to regulate the amount of exposure to sunlight. After a period of exposure, the length of time probably varying with changes in the duration and intensity of sunlight and the physiological condition of the animal, inhibition to activity begins. Because exposure to sunlight is required to maintain normal activity levels, parietal-eye inhibition may function to prevent metabolic excesses and to insure the maintenance of energy reserves. The 'eye' thus may influence the intensity and perhaps also the duration of the life of the animal"--P. 35-36.
40 p. : ill. ; 24 cm.
Includes bibliographical references (p. 36-40).