The maximum temperature that a reptile can tolerate physiologically is ordinarily higher than the maximum temperature tolerated voluntarily (Cowles and Bogert, 1944:277); but, the two maxima may be separated by only a few degrees. Most poikilothormous vertebrates neither tolerate nor long survive body temperatures exceeding 40 degrees (Cowles and Bogert, _op. cit._:269). It is evident (Fig. 22) that ornate box turtles do not often tolerate body temperatures above 33 degrees and that temperatures in excess of 35 degrees are probably never tolerated under natural conditions. At 9:15 A. M. on July 5, 1955, an adult female emerged from mud where she had spent the night (body temperature 28.4°, mud 28.4°, air 30°). After foraging for 40 minutes in bright sunlight on a grassy hillside she had moved approximately 100 feet and her temperature had reached 34.6 degrees (air 33.0°). At 9:56 A. M. she moved rapidly and directly to a den under a rock nearby; 15 minutes later her body temperature had not changed but after 65 minutes it had dropped to 33.4 degrees. The temperature of air in the den was 31 degrees. This female began her activities at nearly optimum body temperature relatively late in the morning and, by foraging intensively for less than one hour, probably was able nearly to satisfy her daily food requirements; by foraging near suitable cover she could remain active until her body temperature reached a critical threshold, and she thereby saved time otherwise required for finding cover or making a form. The following observations, extracted from field notes, indicate that body temperatures near 40 degrees are the approximate lethal maximum and are well above those temperatures voluntarily tolerated by _T. ornata_. On July 4, 1955, a subadult female was in the water at the edge of a pond. The temperatures of the air, water, and turtle were 32.0, 30.6, and 30.2 degrees, respectively. At 11 A. M. the turtle was tethered in direct sunlight on the hard-baked clay of the pond embankment (temperature of air 33.4°). The turtle's response to steadily rising body temperature over a period of 31 minutes is illustrated by the following notes. Body Time (A. M.) temperature Remarks 11:00 33.0 Tethered on slope. 11:05 34.6 Strains at tether in several directions. 11:09 36.5 Tries frantically to get away; draws in limbs and head rapidly and momentarily at any movement on my part, and hisses loudly. 11:13 37.5 Mouth held open slightly; turtle overturns in effort to escape; frantic scrambling resumed a few seconds after I right turtle. 11:17 38.2 Mouth now held open most of the time; white froth begins to appear around mouth.