<ref name="Billen_1993">{{cite journal |first1=J. P. J. |last1=Billen |year=1993 |title=Morphology of the exocrine system in ants |url= |journal=Materialy Kollokviumov Sektsii Obshchestvennykh Nasekomykh Vsesoyuznogo Entomologicheskogo Obshchestva |publisher= |volume=2 |issue= |pages=1–15 |doi= }}</ref>