In October, 1955, nine _T. ornata_ of various sizes, collected in Douglas County, Kansas, were brought to the laboratory for observation under conditions of controlled temperature. They were kept at room temperature for several days and were fed regularly, with the exception of one hatchling that was fed nothing in this period. On October 22 the turtles were placed in a room where the temperature was maintained constantly at zero degrees. One of the nine turtles, an adult female, was killed with chloroform immediately prior to its removal to the cold room. A list of the turtles used in this experiment is given below. Age Carapace Weight class length in mm. in grams 1) Hatchling 33.1 8.4 2) Hatchling[A] 29.9 6.7 3) Juvenile 52.5 29.3 4) Juvenile 50.2 26.1 5) Adult [Male] 125 376 6) Adult [Female] 118 400 7) Adult [Male] 119 386 8) Adult [Female] 110 325 9) Adult [Female] 115 ---- [A] Starved. Turtles were kept in the cold room for periods of 100 minutes (hatchlings and juveniles) and 200 minutes (adults). The entire experiment, including the time in which the turtles were allowed to warm after they were taken from the cold room, covered a period of nearly six hours (375 minutes) during which the turtles were under constant observation. Individual body temperatures were taken continuously in this period (39 for each juvenile and 24 for each adult) in the order that the turtles were numbered; gaps between records of the body temperature of a given individual therefore represent the time required to record temperatures for the rest of the turtles in the group. The rates of rise and fall of temperature for each of the nine turtles considered are shown as a graph in Figure 23. Rate of temperature change was inversely proportional to bulk; hatchlings, for example, cooled and warmed a little more than twice as rapidly as did adults. Rate of temperature change was intermediate in juveniles but was more nearly like that of adults in the warming phase and closer to that of hatchlings in the cooling phase (Table 5). Considering that hatchling no. 2 was smaller than no. 1, the rate of change in its temperature did not seem to be significantly altered by starvation. The adult males showed a tendency to change temperature faster than adult females even though both males were larger than any of the females. The slight difference in rate of temperature change between the sexes (Fig. 23) may have been fortuitous.