88 



Scientific Proceedings (hi). 



40 (1622) 



Differential survival of male and female dove embryos in in- 

 creased and decreased pressures of oxygen: A test of the 

 metabolic theory of sex. 



By Oscar Riddle. 



[From the Carnegie Station for Experimental Evolution, Cold 

 Spring Harbor, N. Y.] 



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 dif- 

 ference was also found in more limited investigations of adults of 

 the two sexes. Our previous work has rather consistently indi- 

 cated 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 com- 

 plete applicability of the metabolic theory of sex to pigeons. 



A 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 C02-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 em- 

 bryos. Similarly — since we had earlier learned that high pressures 



