of egg shells is produced from the shell gland, rather than from the breakdown of erythrocytes in the blood stream, although there is no evidence that the sources of the material are neither tetrapyrroles nor free heme from the blood plasma.

Along with its presence in avian egg shells, other studies have also shown that biliverdin is present in the blue-green blood of many marine fish, the blood of the tobacco hornworm, the wings of moth and butterfly, the