: In birds, after 4–7 days of incubation, a fertilized egg will show dark veins and a small embryo when held up to a bright light (candling).
: In a freshly cracked chicken egg, a fertilized egg is identified by a small, white "bullseye" (blastoderm) on the yolk, rather than a solid white spot (blastodisc). fertilized egg
: Modern methods use non-destructive NIR (near-infrared) spectroscopy to detect subtle metabolic and hydration differences between fertile and infertile eggs before incubation. Biological and Legal Contexts An egg is not a chicken and an embryo is not a child : In birds, after 4–7 days of incubation,