297] NORTH AMERICAN MONOSTOMES 79 



if this reduction is of phylogenetic import or subject to rapid change under 

 environmental stimuli. A comparison of similar worms under different 

 conditions leads to the belief that the sucking musculature is not subject 

 to such rapid and radical change as indicated by Odhner (1907). As shown 

 in an earlier part of this paper, Cyclocoelum wilsoni and Cyclocoelum 

 vicarium from the intestine of their host have poorly developed oral suckers 

 and no trace of an acetabulum while Cohn has found a rudimentary aceta- 

 bulum in Monostomum jlavum, a species which inhabits the trachea. 



In the Heronimidae which inhabit the lungs and especially the larger 

 bronchi of turtles, the oral acetabulum is well developed while any evi- 

 dence of the presence of a ventral sucker has not been obtained. This 

 stands in rather striking contrast to the statement of Odhner (1907) 

 referred to above. Fuhrmann (1904) cites an interesting case in his Bothrio- 

 gaster variolaris which was collected from the intestine of Rostrhamus 

 sociabilis. This species according to the author has a ventral acetabulum 

 but no oral sucker. A pharynx, however, is present. As stated pre- 

 viously his species is strikingly similar to Monostomum oculobium Cohn 

 taken from Vanellus melanogastrus which Cohn (1902) says is devoid of 

 sucking apparatus. Why has the oral sucker of Bothriogaster variolaris 

 atrophied if reduction is due to habitat as stated by Cohn (1902) and 

 Odhner (1907)? 



Another interesting correlation is found among the Notocotylidae and 

 the Pronocephalidae both of which inhabit the intestine. Among the 

 Notocotylidae are forms which late in life develop the ventral holdfast or 

 adhesive glands and those without such glands, both types of which have 

 been found in the alimentary tract of the muskrat. Linton (1910) reports 

 a species Barisomum erubescens from the intestine of three tropical fish 

 which show no sign of any sucking organ save the oral. Of the several 

 genera of the Pronocephalidae taken from the intestine of Chelone midas 

 only Adenogaster shows any trace of accessory adhesive apparatus. On 

 the other hand Odhner (1911) found reason to ally the Angiodictyidae a 

 closely related family to the distomes on account of a weakly developed 

 acetabulum found in Haplorchis carhinus Looss. 



As was stated previously Odhner (1907) proved beyond doubt the 

 presence of both pharynx and oral sucker in Didymozoon scombri Tschbg. 

 but found there no ventral sucker. Four years later Ariola (1906) asserts 

 the Didymozoon nature of Kbllikeria (Distoma) okeni (Kolliker) which 

 he states is synonymous with Monostomum fillicolle Rud. In the Parona 

 material reported as Kollikeria in which there were many distomes accord- 

 ing to this author, he finds a single form without the acetabulum. 



On the other hand Collyriclum faba (Bremser) and Collyriclum colei 

 Ward, other cyst living trematodes, have no acetabula but present, however, 

 a well developed oral sucker. It is difficult to interpret how worms which 



