Observations on the establishment of Polymorphus minutus (Acanthocephala) in the intestines of domestic ducks

No external signs of activation of cystacanths in the alimentary tract were observed until 25 min after oral ingestion. Peak percentage evagination was observed after 60 min. Activation and establishment of cystacanths were never found in the ventriculus or anterior to it, but several crushed specimens were found in the ventriculus, which is a mechanical hazard to the parasite. Infections established by cannulation at the yolk-stalk are greater than infections produced by ingested parasites; thus the ventricular environment does not need to be experienced by the freed cystacanth for activation to take place.