1. Two sex determining mechanisms in reptiles have been observed;(l) the heteromorphic sex chromosomes or heterogametic sex detrminaton,and(2)the environmental sex determination.2. The sex chromosomes are common in snakes and some lizards,.but apparently rare in turtles and absent in corocodilians and the tuatara.3. The environmental sex determination is common in turtles and has been reported with three lizards and alligators.4. Certain extreme environment conditios of affect the phenotype of heterogametic...