Embriologic development of Podocnemis unijilis on wild and laboratory conditions, from nesting, was monitored. Twenty eight phases, occurring in 95 days were identified, including embriogencsis as a normal series. A close relationship between the progressive expansion of a white zone of the egg-shell and the sequence development of the embriologic stages was found. This relationship is thought be useful as a method to identify externally the stage of the em bryo. It was determined that all the eggs of a nest do not hatch simultaneously, possibly because the embryos were seen to be in 4 different stages of development, and their growth is asynchronous. The physical parameters conditioning effective embryogenic process of this chelonia were registered.