Of sixty eggs studied in the laboratory, 45 (75 per cent) were fertile; 36 (80 per cent) of the fertile eggs (those in which the blastodisc was at some time discernible by transmitted light) hatched successfully. In six clutches all the eggs were fertile and five of these clutches hatched with 100 per cent success. One clutch contained eggs that were all infertile and another clutch had four infertile eggs and two fertile eggs that failed to hatch. Among nine fertile eggs that failed to survive, four casualties occurred in the late stages of incubation or after hatching had begun, indicating that these are probably critical periods. Fertility of eggs was not correlated with size or age of female, with size of clutch, or with size of egg. Eggs laid in the laboratory had higher rates of infertility and prenatal mortality than did eggs dissected from oviducts. Handling of eggs in removing them from nests to incubation dishes, after embryonic development had begun, might have been responsible for reduced viability (Table 2). TABLE 2.--Comparative Rates of Fertility and Prenatal Mortality for Eggs Dissected from Oviducts and for Eggs That Were Laid in the Laboratory and Subsequently Removed to Incubation Dishes. ===========================+==============+=============== | Eggs removed | Eggs dissected NUMBER OR PERCENTAGE | from nests | from oviducts ---------------------------+--------------+--------------- Number of eggs examined | 22 | 38 ---------------------------+--------------+--------------- Percentage of fertile eggs | 64 | 82 ---------------------------+--------------+--------------- Percentage of fertile | | eggs hatched | 50 | 94 ---------------------------+--------------+--------------- Percentage of eggs hatched | 32 | 76 ---------------------------+--------------+--------------- Reproductive Potential