Woodcut of conjoined twins from Des Monstres et prodiges by Ambroise Par矇, 1573. Conjoined twins are identical twins born with their bodies joined at some point and having varying degrees of residual duplication, a result of the incomplete division of the ovum from which the twins developed. Des Monstres is filled with unsubstantiated accounts of sea devils, marine sows, and monstrous animals with human faces. With its extensive discussion of reproduction and illustrations of birth defects, the book invited accusations of pornography.