As a rule monogenetic trematodes locate on the body of their 

 host by attaching themselves by the posterior ends, and in normal con- 

 ditions have little relocation movement or even do not change their location 

 at all. Many species, however, are completely deprived of the ability to 

 transfer .either because of a special structural arrangement of their attach- 

 ing apparatus, or as a result of the growth of tissues of the host which sur- 

 round the part of the body of the parasite and finally attach the worm for its 

 entire life to a fixed position (Fig. 108). Under certain conditions, mainly 

 unfavorable ones, many of the small worms (Dactylogyridae , Tetraonchidae 

 and others) as well as the large worms (Monocotylidae , Capsalidae and 

 others) move along the body of their host fairly actively. This transfer 

 takes place with the help of the attaching apparatus of the posterior and 

 anterior ends, and resembles the locomotion of leeches. The worm, which 

 starts to move, first attaches by its anterior end, having stretched it in the 

 direction of movement, and then, having attached itself, draws the entire 



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Fig. 108. Dactylogyrus iwanowi Bychowsky, adult worm sitting on the gills 

 of Leuciscus brandti Wal. from the region of Vladivostok (Sea of Japan). 

 On the left normal gill filament. 



body to the anterior end, again attaches itself by the posterior end, and re- 

 peats the same nnotion (Fig. 109). It is not without interest to note that the 

 strength of attachment of monogenetic trematodes by means of the anterior 

 and especially the posterior end is very great. Thus, Dactylogyridae, which 

 have been isolated into a saltshaker (some type of experimental vessel-- 

 perhaps similar to a stender dish?, nobis) and which have attached themselves to 

 it, withstand a fairly strong stream ot water from a pipette; apparently the 

 attachment results from a sticky secretion of the glands from the posterior 

 end of the body because the hooks cannot play a significant role under such 

 conditions. Certain large forms, for instance Nitzschia sturionis (Abild- 



gaard), which have a powerful sucker attach themselves with such force that 

 it is easier to tear the worm in two than to piill it from its place of attachment. 



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