A number of changes in structure and appearance occur in the period from hatching to puberty. Fontanelles of the bony shell close at or before puberty. Movable parts of the plastron are not functional until the fourth year. Markings on the carapace change from a series of dots to distinct, straight-sided radiations, and a similar pattern develops on the plastron. Markings on the heads of females resemble those of juveniles but males have greenish heads. Males further differ from females in having a red iris, more brightly colored antebrachial scales, and a turned in first toe. Analysis of some 500 body temperatures (Centigrade) obtained under natural conditions revealed the following: the optimum temperature for activity is near 30 degrees; box turtles emerge from cover usually when body temperature is 24 degrees or higher, and almost never when the body temperature is below 15 degrees; body temperature is raised to optimum by basking in open areas although activity begins at suboptimum temperatures if basking is impossible; cover of dens, burrows, or forms is sought when the body temperature rises above 30 degrees; and, maximum and minimum body temperatures that would be lethal to box turtles (for prolonged periods) are approximately 40 and zero degrees, respectively. Laboratory experiments showed speed of response to environmental temperature to be inversely proportional to bulk; hatchlings could be chilled or warmed more than twice as fast as adults and were active within a narrower range of temperature. Ornate box turtles in general are subject to a narrower range of thermal activity than are aquatic turtles that occur in the same areas. Box turtles are dormant approximately five and one-half months of the year--from late October to mid-April. Warm weather in November and late March sometimes stimulates temporary activity but dormancy is uninterrupted from mid-November to early March. Forms, dens, and burrows are used as hibernacula. Depth of hibernacula is dependent on severity of temperatures and amount of vegetational cover; hibernacula in open grassland were seven to 18 inches deep whereas those in wooded areas were six inches or shallower. Box turtles are ordinarily solitary when hibernating. Injuries and deaths due to freezing probably occur in the coldest part of the winter. The lowest body temperature of a turtle that survived a winter was 2.7 degrees; an individual, the temperature of which was nearly zero for several days, subsequently died. Turtles burrow upward at the end of hibernation and remain just below the surface for a week or two before emerging. The primary stimulus for emergence seems to be a period of warm moist weather.