Critical Periods and Causes of Death in Avian Embryonic Development

ARIAN embryonic mortality has long been a subject of biological interest. It is also a problem oœ obvious economic importance. The total embryonic mortality of domestic fowl, Gallus gallus, has been progressively increasing for some time. Less than 30 years ago, when flocks were small and kept at large, the embryonic death rate rarely exceeded i0 per cent. As simple and primitive methods of poultry management have been replaced by such efficient modern practices as intensive feeding, breeding in confinement, and largescale artificial incubation, embryonic mortality has frequently risen to 25 per cent or more. Numerous investigations have attempted to determine the causes of death during the incubation period, and to explain the rising embryonic death rate. Studies have been made not only of chickens, but also of a number of other domestic birds and some game birds raised in captivity.