Thermal patterns in the heating and cooling of Iguana iguana and Ctenosaura hemilopha

1. 1. Temperatures were measured from cloacal, head, heart, lungs, nostrils and lumbosacral regions of Iguana iguana and Ctenosaura hemilopha as the animals were radiantly heated and allowed to cool. Duration, intensity, area heated and angle of incidence of the heat source were varied. 2. 2. Results were expressed in terms of a modified time constant. Time constants during a typical exposure were ranked as follows: cloaca, head, heart and lung. 3. 3. Nostril time constants suggest countercurrent heat exchange in the upper airways. 4. 4. The time constant for head heating did not differ appreciably from that of the cloaca, indicating a lack of cranial heat sequestration.