(1) The loggerhead turtle, Caretta caretta (Linn.), on hatching weighs about 20 grams and its carapace measures approximately 4.8 centimeters in length by 3.5 centimeters in width. (2) An individual reared in confinement at Key West, Florida, when four and a half years old, weighed 37 kilograms, or a little over one fourth the average adult weight. Its carapace measured 63 centimeters in length and 59 centimeters in width. Its rate of growth was several times more rapid than that shown by three other loggerhead turtles reared under almost similar conditions. Even these lower rates, however, indicate that turtles grow to maturity much more rapidly than is generally supposed.