The Gaseous Environment of the Chick Embryo in Relation to Its Development and Hatchability

IN CONTINUATION of experiments designed to determine the effect of various levels of CO2 and O2 upon embryonic development and hatchability, test conditions have been imposed for the 96 hr. period from the beginning of the 13th to the end of the 16th days of incubation. In the previous reports of this series (Taylor et al., 1956; Taylor and Kreutziger, 1965; 1966) a progressive increase in tolerance to higher levels of CO2 with continued incubation of the egg has been demonstrated in each succeeding test period. With respect to increasing levels of O2, an early tolerance was followed by a decreased resistance during the 5–8 day incubation period, and then by a reversal of trend during the 9–12 day period toward an increased resistance which, however, did not reach the levels obtained during the first 4 days of incubation. Development of the chick during the period of the…