Abstract
A comparative study has been made of certain species of Diphyllobothrium which are primarily parasites of birds, but which have been obtained from man and other hosts, both naturally and experimentally. As a result of this work it appears that only two valid species are known in birds, namely: Diphyllobothrium dendriticum (Nitzsch, 1824) and D. ditremum (Creplin, 1825). These species differ markedly from each other in certain morphological features and there appears to be a noticeable difference in their host-adaptation, inasmuch as D. ditremum occurs only in birds belonging to the families Phalacrocoracidae, Ardeidae, Colymbidae and Anatidae, while D. dendriticum occurs naturally in birds belonging to the Laridae and other families, and experimentally also in mammals.