Pearse, A.G. (1969). "The cytochemistry and ultrastructure of polypeptide hormone-producing cells of the APUD series and the embryologic, physiologic and pathologic implications of the concept". J. Histochem. Cytochem. 17 (5): 303–13. doi:10.1177/17.5.303. PMID4143745. S2CID8240028.
Pearse, A.G. (1969). "The cytochemistry and ultrastructure of polypeptide hormone-producing cells of the APUD series and the embryologic, physiologic and pathologic implications of the concept". J. Histochem. Cytochem. 17 (5): 303–13. doi:10.1177/17.5.303. PMID4143745. S2CID8240028.
Pearse, A.G. (1969). "The cytochemistry and ultrastructure of polypeptide hormone-producing cells of the APUD series and the embryologic, physiologic and pathologic implications of the concept". J. Histochem. Cytochem. 17 (5): 303–13. doi:10.1177/17.5.303. PMID4143745. S2CID8240028.