yes there are 2 of them you are correct. The thinner one by the chick has veins and carries the chicks blood supply untill the yolk is absorbed. that chick was not fully developed and looks like it died about 2-3 days before it should have hatched. If the eggs were in there for the full 21 days it either died a couple days before hatch OR your temps were to low and the chick never really fully developed by day 21.