241] NORTH AMERICAN MONOSTOMES 23 



Taschenberg) and just posterior to it a very small muscular bulb the phar- 

 ynx. Odhner (1907) finds in Didymozoon scombri Tschbg. a similar pharyn- 

 geal bulb which he figures and proves beyond doubt that the pharynx of 

 Taschenberg is a very strongly developed sucker followed by an extremely 

 small pharynx. In this same notable work he says that in Cyclocoelum 

 (Monostomum) mutabile (Zeder) and other parasites where only a pharynx 

 is present that there is always a region anterior to it which he terms the 

 "Mundrohr" or "Mundhohle" (prepharynx of Monticelli), a structure 

 which by the contraction of the inner walls changes the pharynx into a 

 sucker. This same region is shown in the figures of Odhner for Didymo- 

 zoon scombri Tschbg. 



Looss (1899) speaks of the mouth sucker but gives no equivalent for 

 the pharynx of Monticelli. Later, however, he interprets the swelling at 

 the beginning of the esophagus in Microscapha reticularis as a pharynx. 

 Cohn (1904) calls this to account when he states that this swelling is 

 nothing more than the esophageal sphincter which is present in many 

 species. The same author interprets the oral sucker of Looss, or buccal 

 bulb (anterior sucker) of Van Beneden, as a pharynx and adds that it is 

 his opinion that soon monostomes will be found with a well formed sucker 

 adjoining a typical pharynx. The evidence given in support of this con- 

 sists of the statement that Haplorchis cahirinus Looss has a strongly devel- 

 oped pharynx preceded by a rudimentary sucker and that he has observed 

 in Cyclocoelum (Monostomum) mutabile (Zeder) and in one other species 

 (to be published later) a rudimentary sucker. On the contrary Looss 

 (1899) figures Haplorchis cahirinus with a well developed but small oral 

 sucker followed by a somewhat smaller but perfectly developed pharynx 

 and in his description of this species states specifically that the oral sucker 

 and the pharynx are well developed structures. He regards the rudimentary 

 structure occurring on the ventral side as an acetabulum. He adds also 

 that the nerve commissure which according to Braun lies in all the Digenea 

 more or less bent around the dorsal side of the oral acetabulum and the 

 pharynx, is in front of the muscular sucking organ in the Monostomidae 

 and therefore that organ is a true pharynx, tho this organ serves both as a 

 sucker and a pharynx. 



Stossich (1902) calls the pharynx of Monticelli an "inner sucker" which 

 he says serves the same function as the mouth sucker of other trematodes. 

 Odhner (1907) states that those that acquire holdfast organs in the 

 least degree are the parasites of the respiratory organs; the group contain- 

 ing Cyclocoelum mutabile being entirely suckerless. Kossack following the 

 decision of Monticelli says that the question can be determined only by 

 a study of the position and distribution of the nerve ganglia. Conse- 

 quently he termed the anterior muscular structure a true pharynx. Ward 

 (1918) calls the same structure the oral sucker and says that no pharynx is 



