DISTOMA OPHTHALMOBIUM. 191 



tliinks he lias liit upon tlie juvenile form of Distoma lanceolatum in 

 the body of Planorbis marginatus, but his feeding experiment to prove 

 tins relationship was not thoroughly satisfactory. Future investiga- 

 tion will doubtless reveal all the actual stages through which this 

 and many aUied fluke-species pass during their progress upwards 

 from the lowest larval to the highest sexually-mature condition. 



3. Distoma ophthalmobium. 



D. ophthalmobium, Diesing : Kuchenmeister ; etc. 



D. (lentis), Yon Ammon. 



D. ocuU-humani, Gescheidt. 



Dicroccelium ocuU-humani, Weinland. 



? Monostoma lentis, Nordmann ; Gescheidt ; Diesing ; etc. 



? Festucaria lentis, Moquin-Tandon. 



I here combine the two so-called species of human eye 

 trematodes under one title, without, however, for a moment sup- 

 posing that we have either in the Distoma ophthalmoUum of Diesing 

 or the Monostoma lentis of Nordmann, a genuine sexually-mature 

 fluke. I think it highly probable that both forms may be the 

 young of one distome ; and (as suggested by Leuckart's compari- 

 sons in the case of Distoma ophthalmobium) it is quite possible they 

 may both of them be referable to the species last described {D. 



Tig-. 41. — The so-called Distoma opMhalmohiwm ; considerably magnified. — Von Ammon. 



lanceolatum). Certainly one has a difficulty in believing that so 

 accurate an observer as Nordmann could have overlooked a ventral 

 sucker, if one were really present ; and yet, on the other hand, the 

 remarkable minuteness of the worm may have served to obscure 



