Like other reptilian eggs, those of the racer are dependent upon the warmth of their surroundings for incubation. They are tolerant of a wide range of environmental temperatures, but the higher the temperature the more rapidly incubation proceeds. Under natural conditions there may be much difference in hatching time in two clutches laid at the same time and in the same locality. Site of the nest--deep and well insulated, or shallow; in a well shaded situation or one exposed to maximum amounts of sunshine--would largely control rates of development. Clark (1949:249) writing of the subspecies _anthicus_ in north-central Louisiana, stated: "eggs are laid about the first of June.... young begin to make their appearance at about ... July 1." Even for the southern states these dates of laying and hatching seem somewhat too early to reconcile with the records published by other observers, and are in need of verification, especially since they seem to be based upon vaguely remembered observations rather than upon written records. At the other extreme Surface (1906:167) wrote of _constrictor_ in Pennsylvania that hatching may occur as late as October, and that there is evidence some young may even remain in the egg over winter before hatching occurs. Several incubation periods are on record for clutches laid and hatched in captivity, as follows: _C. c. mormon_, Oregon, 47 and 51 days (laid July 3, 1961, hatched August 19 and 23; Van de Velde, Martan and Risley, 1962:212). _C. c. stejnegerianus_, Texas, 73 days (laid June 5, 1947, hatched August 17, Auffenberg, 1949:54). _C. c. priapus_, S. Illinois, 58 and 59 days (laid July 10, 1940, hatched September 6 and 7, Cagle, 1942:187). _C. c. flaviventris_, Kansas, 50 days (laid July 4 and 5, hatched August 23 and 24; Munro, 1950:124). _C. c. flaviventris_, Texas, 43 days (laid June 9, 1952, hatched July 22; Guidry, 1953:50). No incubation periods for eggs in natural nests have been recorded. In the course of my study, eggs obtained from 12 captive females were hatched in confinement, with an average incubation period of 51 days (43 to 63) as follows: Laid July 6, 1955, hatched August 20. Laid July 3, 1958, hatched September 3 and 4. Laid June 21, 1959, hatched August 17. Laid June 26, 1959, hatched August 17. Laid July 7, 1959, hatched August 23 to 25.* Laid June 23, 1960, hatched August 20.* Laid June 30, 1961, hatched August 30. Laid July 15, 1961, hatched September 1 and 2.* Laid July 18, 1961, hatched September 2 and 3.* Laid July 4 and 5, 1962, hatched August 15 and 16.* Laid June 29 and 30, 1962, hatched August 14 and 15.* Laid July 6, 1962, hatched August 16 to 20.* In the foregoing list those entries marked with asterisks were obtained from the Harvey County study area; all others were from the Reservation and Rockefeller Tract. _Hatching_