THE LIFE HISTORY OF PARORCHIS AVITUS (LINTON) A TREMATODE FROM THE CLOACA OF THE GULL

The life history of Parorchis avitus has been experimentally traced. The cercariae occur in the marine snails, Urosapinx cinereusand Thais (Purpura) lapilius. Adults have been obtained from the cloaca of the common tern, Sterna hirundo, and the roseate tern, Sterna dougalli, after feeding the young birds with encysted larvae.It has been shown that a specific secondary intermediate host is not essential for the completion of the life history; only a means of transference is necessary.Additional morphological differences between Parorchis avitus and Parorchis acanthus are described.