The pyramidal cells of the interior part of the pharynx of the Gyrodactylidae 

 possess great mobility and can powerfully extend and contract. Their 

 function is not known, but apparently they have a certain relationship to 

 the pulling off of the epithelial cells of the host during feeding. 



Among monogenetic trenna- 

 todes the esophagus for the most 

 part is short or may be completely 

 absent. Among forms with relatively 

 long esophagi it often forms lateral 

 blind outgrowths which can branch 

 strongly. In other cases, the esopha- 

 gus has the appearance of a straight 

 pipe and changes directly into the 

 intestinal tract. Among many forms, 

 the presence of a powerful muscular 

 sphincter, the contraction of which 

 interrupts the passage of food into 

 and out of the tract at the beginning 

 of the esophagus, is characteristic. 

 Numerous monocellular glands, 

 which are observed in certain Mono- 

 cotylidae, can open into the esopha- 

 gus. It is interesting that these glands 

 are absent among the highest monogenetic trematodes, for instance among 

 Microcotylidae and Hexabothriidae, Goto also calls these glands "salivary. " 



0.1 HM 



Fig. 61. Nitzchia sturionis (Abild- 

 gaard), cross section through the 

 pharynx of the worm, from the 

 buccal cavity of Huso huso (L. ) 

 near the Island of Sara (Caspian 

 Sea). 



Intestine. The intestine of monogenetic trematodes historically p. 47 

 evolved from the sac -like one of Rhabdocoela and during the individual on- 

 togeny also iindergoes a similar stage (see the chapter on embryology) and 

 is characterized by the absence of an 

 anal opening. Usually the intestine 

 has the appearance of two trunks 

 stretching along the entire body, 

 less often it is simple in the form 

 of a more or less long pipe (Tetra- 

 onchidae, Figs, 29, 64; Tetra- 

 onchoididae. Figs, 29; and certain 

 others). The two -branched intes- 

 tine can be of varied shape. Intes- 

 tinal trunks can be smooth in the 

 shape of cylindrical pipes and end 

 blindly (Gyrodactylidae, Fig. 12, 

 a number of Ancyrocephalinae 

 etc. ), or they can have a number 

 of lateral growths and branches 

 along their length and finally. 



Fig, 62, Polystonna integerrlmum 

 Froelich, frontal section of the 

 anterior part of the body. Salivary 

 glands appear dark. 





41 



