eggs are candled to observe the development of the embryo. the air pocket and veins are clearly visible inside the egg.

egg observation duckling eggbearing development duck veins incubator embryo lamp shining poultry heart incubation observing inside developing darkness incubated candling brooding brooder light baby breeding animal red hatchling growing new unborn vasculogenesis biology yolk research lab bird natural farm agriculture breed closeup yellow domestic brightly