DR. THEODUK NEUMANN. 239 



again progeny ; its grandchildren or great-grandchildren 

 meet perhaps the other one which had been waiting pa- 

 tiently until it might find favorable conditions. The 

 younger one lives besides the old one ; they equal each 

 other perfectly ; and yet one belongs to a time long past, 

 which flowed by without leaving any traces, the other 

 one belongs to the offspring of another that fell to pieces 

 long ago. 



In numerous cases there may be a third intermediate 

 host for a third entirely different generation, which also 

 produces germs. 



In other instances the sporocysts remain small and 

 baglike, the number of the germs within is only small, 

 and no cercarife originate from them. Instead of these 

 with their flat bodies, forked alimentary canal and mov- 

 able paddle-tail, we see forms of cylindric shape*, more 

 or less elongated, hose-like, with simple tubular intes- 

 tines. Their movements are mostly creeping, slow and 

 sluggish; they do not leave the snail-liver, but grow up 

 in it. This form has been called "redia" in honor of the 

 Italian scientist Redi. So we have here three genera- 

 tions: the sexual animal, the sporocyst and the redia. 

 The latter two are the nurse generations, the redia the 

 proper nurse, the sporocyst the grand-nurse. 



The germs formed in the redia nearly all develop into 

 cercarise, some however into so-called daughter-redise, 

 which remain at home while the cercarise emigrate. 

 The daughter-redise again give birth to cercarise and 

 redise, and thus we may find a whole series of genera- 

 tions, forms which look alike, but which are by no 

 means so closely and plainly related to each other, but 

 present greater complications than can be stated in a 

 few words. How seasons affect this production of redise 

 and cercarise may be studied in the distomum hepaticum, 

 the liver-fluke, which produces a very dangerous, usually 

 fatal, disease of the sheep. It has also been observed in 



177 



