In the course of a series of experiments designed to investigate the conditions necessary to hatch pheasant (Phasianus colchicus) eggs by artificial incubation, the author found it necessary to establish the chronological appearance of aging criteria throughout the incubation period. The data collected deal with external characteristics visible without dissection, and are described herewith in nontechnical language.
No takes yet. Share an insight, caveat, or question.
R. J. Fant (1957) studied this question.