16 THE INTERNAL PARASITES OF 



condition is termed a pupa, which is the highest sexually 

 immature stage of fluke development. In this advanced 

 condition it becomes encysted in the body of the water 

 snail or intermediary bearer ; being afterwards tranferred 

 to its ultimate host, within whose intestinal canal it is at 

 length transformed into the perfect amphistome. Yery 

 much more might be said on this subject, but I fear to 

 complicate my record of the developmental phenomena 

 exhibited by flukes. Whilst the larger features of this 

 strange kind of metamorphosis are tolerably uniform 

 throughout the trematode group, the lesser modifications 

 of plan by which these creatures reproduce and multiply 

 without intercourse are practically infinite. It is worthy 

 of note, however, that external causes, such as excessive 

 heat and moisture, lie at the root of the matter, so that 

 the multiplication of flukes during particular seasons is 

 readily accounted for. 



Only by the precise enunciation of such facts as these 

 can it be hoped that our agriculturists will be duly im- 

 pressed with the practical importance of researches in 

 helminthology. With these data before them, they can- 

 not deliberately refuse to recognise the now well-esta- 

 blished truth that cattle and other ruminating animals 

 become infested with flukes — distomes, amphistomes, 

 fascioles, and what not — in a direct manner when they 

 drink from ponds, stagnant pools, and even running 

 streams of water. It is probably not necessary that the 

 pond snails themselves should be swallowed, seeing that 

 the free-swimming cercarise appear to be able to complete 

 their flake development without passing through the 

 encysted pupal stage within the bodies of their inter- 

 mediary bearers. In the case of the amphistomes it is 

 almost certain that the free tailless cercarige, when thus 



