CHAPTER II 



THE MORPHOLOGY OF THE TREMATODA, 

 OR FLUKES 



TECHNICAL SUGGESTIONS 



For demonstration of the monogenetic flukes, species of the well- 

 known genus Polystomum may be found in the mouth and the urinary 

 bladder of various turtles, or in the urinary bladder of our native tree 

 frogs. Specimens of the best-known species, P. integerrimum, can be 

 purchased from European dealers. The minute Gyrodactylidse may 

 be secured from the gills and skin of various fish. 



For study of the anatomy of a digenetic fluke, the commonly used 

 sheep liver fluke is so complicated as to be wholly unsuitable for 

 beginners. Little better are the various lung flukes of frogs which are 

 often substituted. Much more suitable species are Opistorchis 

 pseudofelineus from cats and Clonorchis sinensis from the liver of man. 

 Prepared slides of the latter are now readily available from dealers and 

 we shall use them as a type. In default of both, the immature 

 Clinostomum from the flesh of perch and other fish, or from frogs, may 

 be used. Study of the simpler forms may be followed by that of the 

 frog lung flukes and the sheep liver fluke. 



CHARACTERISTICS OF THE TREMATODA 



The Trematoda, or flukes, are exclusively parasitic flatworms 

 (Platyhelminthes) , often leaflike in shape, without a covering 

 of cilia in the adult state. They possess a well-developed ali- 

 mentary canal with but one opening, the mouth, at the cephalic 

 end of the body. Suckers are developed on the ventral surface 

 and in the region of the mouth, their position and structure 

 being of much systematic value. With rare exceptions (blood 

 flukes) trematodes are hermaphroditic. 



The class is divided into two subclasses, the Monogenea 

 and the Digenea. As indicated by the names, the monogenetic 

 flukes develop directly, on a single host, while the digenetic 

 forms require two or more host species for their development. 



PRACTICAL WORK 

 Polystomum sp. — As an illustration of the more primitive 

 flukes, or Monogenea, there will be demonstrated a representa- 



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