The researches on Monogenoidea were carried out in many 

 different ways, from the point of view of biology, morphology and embry- 

 ology. We gave special attention to wOrk on live materials because it was 

 possible to discover a whole series of structures only in this fashion. 

 Thanks only to the study of live materials was it possible to understand the 

 physiological meaning of a series of morphological peculiarities unknown 

 until the present time. We would also like to underline this circumstance 

 On the strength of the fact that at the present time the study of monogenetic 

 trematodes is based almost entirely upon fixed material which is completely 

 wrong and in many cases leads to erroneous results. It is curious that the 

 researches of the middle of the last century widely utilized live materials, 

 and in many cases their works describe the forms and structure of mono- 

 genetic trennatodes much more precisely than corresponding data of con- 

 temporary authors who are armed with complete microscopic technology 

 but who do not employ direct observation of living Organisms. 



Unfortunately, we could not utilize the data concerning geo- 

 graphical distribution of monogenetic trematodes because there is still 

 very insufficient data at the present time, and this could have led to faulty 

 conclusions. However, in certain isolated cases distribution was taken into 

 consideration. 



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