Chronology and morphology of temperature-dependent sex determination.

Temperature sensitivity and gonadal differentiation were studied in a turtle, Trachemys scripta, with temperature-dependent sex determination. Sex determination was sensitive to both the duration and magnitude of incubation temperature. Temperature exerted an "all or none" effect on the ovarian or testicular nature of most gonads, but affected the length of ovaries in a graded fashion. Collectively, the results indicate that sex determination is controlled by the quantitative effect of temperature during a period beginning prior to (histologically detectable) sexual differentiation and extending to a time when initial sex specific changes are evident in the gonads.