The pineal gland and geographical distribution of animals

A detailed analysis of the occurrence of parietal eye component of the pineal complex in families of lizards has revealed that those in which the parietal eye is absent in most genera (e.g. Gekkonidae, Teiidae) tend to be restricted to low latitudes, whereas families in which the parietal eye is present in most of the genera (e.g. Agamidae, Iguanidae) extend to higher latitudes. Those few genera which lack parietal eyes in the families where the very great majority have parietal eyes are confined to ranges rather close to the equator. The parietal eye may be important in thermoregulatory or reproductive adaptations at higher latitudes where seasons are more severely varied than at lower latitudes. A pineal body is reported to be absent in crocodilians, edentates and, perhaps, dugongs. All these animals tend to inhabit tropical regions. In contrast, seals and walruses have remarkably large pineal glands and are found at very high latitudes. These few fragments of information cannot be used to support any conclusions, but they do suggest that it might be productive to consider the pineal complexes of animals in the context of their geographical distribution.Studies by the author supported by NIH grants NS-08554 and NS-12257.Presented during the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, USA.