Abstract
Summary
1. Parietalectomized lizards (Sceloporus occidentalis), free living in the field, presented evidence of above-normal thyroid activity in animals collected in winter and spring, but not in summer. 2. An annual cycle of thyroid activity is exhibited by both parietalectomized and sham-operated lizards. 3. Thyroid hypertrophy induced by 3 weeks of constant temperature (35°C) is mediated by the hypophysis.
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