293] NORTH AMERICAN MONOSTOMES 75 



in these families; in the Cyclocoelidae it is composed primarily of a large 

 half-moon shaped bladder and ramifying network of anastomosed tubules. 

 In the Notocotylidae a single club-shaped bladder extends almost to the 

 ovary and sometimes a little posterior to the excretory pore (Notocotylus 

 quinqueserialis) ; at the anterior end of this bladder two branches are given 

 off which pass lateral to the ovary and from these numerous side branches 

 are produced. In the Heronimidae the bladder consists of a large median 

 sac with the pore in the anterior dorsal region, while in the Collyriclidae 

 the bladder is single, club-shaped, and branches near the center of the 

 body. In regard to the digestive system equally striking differences appear. 

 The Notocotylidae show no trace of a pharynx while the Cyclocoelidae, 

 Heronimidae and the Collyriclidae possess both sucker and pharynx. The 

 crura of the Cyclocoelidae anastomose in the posterior end of the body 

 while in the other families under consideration the crura end blindly. 

 Another characteristic difference is the presence of dermal glands in some 

 of the Notocotylidae, while such organs are unknown in the other families. 

 In the genital system are to be found equally great characteristic differ- 

 ences in the position of the glands with respect to the intestinal crura as 

 well as in the form of the glands themselves. These and other important 

 differences seem to indicate that these families have arisen from different 

 lines. 



THE APPARENT RELATION OF THESE FAMILIES TO OTHER GROUPS 



Since the great diversity of structure in this group seems to indicate 

 that the monostomes have arisen from different sources, there remains to be 

 considered in conjunction with this fact the close affinity of certain of these 

 families to widely separated groups. 



The finding of a rudimentary acetabulum in Monostomum flavum 

 Mehlis by Cohn and of the well developed acetabulum in Bothriogaster 

 variolaris by Fuhrmann in the same year together with the similarity in 

 structure seems to indicate a relationship to the Fasciolidae through the 

 Syncoelinae according to Fuhrmann (1904) to which Bothriogaster is 

 most closely related. 



After a similar manner the Notocotylidae find their closest parallels 

 among marine forms where the genus Notocotylus has anatomically a very 

 close relative in Adenogaster serialis while those Notocotylids without the 

 ventral glands appear more like the genus Glyphicephalus. 



The Heronimidae stand alone in their organization and do not show 

 close relationship to any known trematodes. 



Attention was first called to the distome character of Collyriclum faba 

 by Braun (1892) and again by Kossack (1911:577) who points out the 

 relation of this species to Distomum gastrophilum but hesitates to decide 

 whether it is a natural one, thus: "Indessen wage ich es vorlaufig noch 



