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Several kinds of evidence have been accumulated which indicate a metabolic difference between the ova (egg-yolks) which give rise to the two sexes in doves. A corresponding difference was also found in more limited investigations of adults of the two sexes. Our previous work has rather consistently indicated that female-producing eggs and female adults have a lower metabolism, males a higher metabolism. Since no metabolic studies upon male and female embryos have hitherto been made this study was carried out as a further necessary test of the complete applicability of the metabolic theory of sex to pigeons.\ud\udA method or means of measuring the metabolic differences between embryos of the two sexes is an enormously difficult thing to devise; and probably no plan is devisable at present which does not involve very much work. The many sources of error and difficulty in any attempt to measure heat-production, O2-consumption of CO2-production became embarrassingly evident when the unmeasurable and continually changing mass of the embryonic tissue is considered. The plan adopted by us was to subject—during one complete year—all or practically all of the embryos produced by the ring-doves and common pigeons of our collection to reduced and increased concentrations of oxygen (or to expose them to protracted periods of cold) and make such measurements and records as would probably reveal any relation of sex to survival under these conditions. Theoretically, if female embryos have a lower metabolism, i.e., lower minimum oxygen requirement than males, the female embryos should withstand diminished pressures of oxygen somewhat better than male embryos. Similarly—since we had earlier learned that high pressures of oxygen result in the death of some embryos—the male embryos should be somewhat better able than female embryos to withstand an increased concentration of oxyge

Differential survival of male and female dove embryos in increased and decreased pressures of oxygen: A test of the metabolic theory of sex