One version of the myth about the barnacle (Branta "anas" leucopsis) and brant (Branta bernicla) geese is that these geese emerge fully-formed from goose barnacles (Cirripedia). There are other myths about how the barnacle goose breeds. The basis of all the myths is that the bird, Branta leucopsis, emerges and grows from matter other than bird eggs. There are many sources to the myth. The etymology of the term "barnacle" suggests Latin, Old English and French roots. There are references in pre-Christian books and manuscripts – some Roman or Greek. Further reference can also be found in an earlier pre-Christian period. The main vector for the myth into modern times was monastic manuscripts and in particular the Bestiary. The myth owes its long standing popularity to an ignorance of the migr