Despite folklore to the contrary, there is no detectable nutritional difference between unfertilized and fertilized eggs. By the time a fertilized egg is laid, the single germ cell has divided into tens of thousands of cells, but its diameter has only grown from 3.5 millimeters to 4.5, and any biochemical changes are negligible. Refrigerated storage prevents any further growth or development. In the U.S. grading system, any significant development of the egg— from minute blood vessels (which appear after two to three days of incubation) to a recognizable embryo—is considered a major defect, and automatically puts it in the “inedible” category. Of course this is a cultural judgment. In China and the Philippines, for example, duck eggs containing two- to three-week embryos are boiled and eaten, in part for their supposed contribution to virility. Because embryos obtain some nourishment from the shell, these duck embryos do contain more calcium than the eggs that they developed from.