363] NORTH AMERICAN PARAMPHISTOMIDAE—STUNKARD 83 



structure he argues that the monostome family Angiodictyidae is really 

 a subfamily of the Paramphistomidae. He shows essential morphological 

 agreement between Distoma quadrangulum Daday and the fish amphis- 

 tomes. His examination of the original specimen of Aspidocotyle con- 

 firms the statement of Braun (1879-1893) that this form belongs to the 

 amphistomes, altho its relation to the other members of the group is 

 uncertain. Further he states that the Gasterostomidae by the structure 

 of the cerearia as shown in the oral sucker and the presence and relations 

 of the oral evaginations, doubtless belongs to the Paramphistomidae. 

 His derivation of the gasterostomes thus from amphistome-like forms of 

 frogs is plausible since the frogs serve as food for the hosts of the 

 gasterostomes. To Odhner's argument may be added that the divided 

 condition of the body in Gastrodiscus recalls the similar condition in 

 certain Aspidogastridae and suggests a possible relationship between 

 these forms. The morphological comparisons of Odhner and other 

 writers appear to show very clearly that divergence and convergence 

 have both had great influence on the phylogeny of certain trematode 

 families. 



