2. July 10, 1952 Egg from natural nest (15.0 × 10.5 mm., .95 gm.) put in refrigerator at 11.6°C. Control (14.5 × 10.6 mm., .8 gm.) from the same clutch kept in hatching medium in laboratory. July 13, 1952 Control egg hatching; refrigerated egg shows no indication of hatching. July 14, 1952 Experimental egg 15.8 × 10.8 mm., 1.0 gm., seems to be in good condition. Nest from which it was taken found to have all remaining eggs hatching today. July 19, 1952 Experimental egg 15.0 × 10.0 mm., 1.0 gm., removed from refrigerator and transferred to container in damp rotten wood in laboratory. Seems to be in good condition. July 23, 1952 Experimental egg found to be hatched this morning, and hatching must have occurred either in the night or late yesterday. Eggshell still damp and pliable. 3. July 10, 1952 Egg from natural nest (14.0 × 10.5 mm., .8 gm.) put in refrigerator at 11.2°C., in container with damp decayed wood. Control egg (14.2 × 10.1 mm., .8 gm.) from the same clutch kept in the same hatching medium in the laboratory. July 12, 1952 Nest from which experimental and control eggs were taken has started to hatch, and two hatchlings were seen there. July 13, 1952 Control egg hatched. July 14, 1952 Experimental egg 14.2 × 10.1 mm., .8 gm., seems to be in good condition. Nest in field examined and all eggs were hatched, with only three of the hatchlings remaining, the others having dispersed. July 19, 1952 Experimental egg 14.0 × 10.0 mm., .95 gm., still appears to be in good condition; removed from refrigerator and kept in laboratory. July 23, 1952 Experimental egg found to be hatched, and hatchling active although still in hiding beneath rotten wood. Probably it hatched early in the day of July 22; the empty shell is still moist. These experiments seem to show that, in the later stages of incubation at least, lowering of temperature to 11° or 12°C. almost halts development of the fetus. Harm does not necessarily result, however, and when again warmed to normal incubation temperatures, the eggs eventually hatch, the incubation period being lengthened by a time approximately equivalent to the interval of refrigeration.