DISTOMA OPHTHALMOBIUM. 191 



thinks lie lias hit upon the juvenile form of Distoma lanceolatum in 

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

 this relationship was not thoroughly satisfactory. Future investiga- 

 tion wiU doubtless reveal all the actual stages through which this 

 and many allied 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. Qentis), Von Ammon. 



D. oculi-humani, Gescheidt. 



Dicroccelium oculi-humani, "Weinland. 



? Monostoma lentis, Nordmann ; Grescheidt ; 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 ophthalmobium 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. 



Fio. 41. — The BO-called Distoma ophthalmobium ; 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 



