46 BNTOZOA. 



there are accessory horny developments in connexion ■with the male 

 reproductive apparatus. 



The general organization of Gyrodactylus has been fuUy eluci- 

 dated by Continental writers, and more especially by the indepen- 

 dent investigations of JSTordmann, Siebold, Guido Wagener, Yan 

 Beneden, and "Wedl, from whose combined experience we have, 

 at length, arrived at the most satisfactory results. As "Wedl's 

 conclusions are summarized within a small compass, I shaU 

 here, instead of offering minute details of any one particular 

 type, subscribe his final account of the principal characters of 

 this group :* — 



a. " Oyrodadylus is found on the gills of fresh- water fishes under 

 numerous specific forms, G. elegans being also found by Oreplin and 

 Siebold on the fins. Moreover, as I have found nearly every species 

 of fish supporting a particular gryodactyle-representative, it would 

 seem that each finny creature supplies its own Gyrodactylus. Some- 

 times two of them are parasitic upon the same giU, being fi'equently 

 associated with Trichodince, as well as with the stUl unintelligible 

 Psorospermice. ' ' 



b. " The clasping apparatus at the posterior end of the body 

 must — in an animal so soft and constantly exposed to the passage 

 of regular currents — be comparatively strongly developed and 

 accommodated to the peculiar dwelling-places ; and probably the 

 varying character of the latter supplies a reason why there should 

 be so great a difference in the mechanism of the hooks belonging to 

 the disk. 



c. " The hooked apparatus affords a very valuable and mathe- 

 matically precise means of diagnosis in the determination of 

 species. This differentiation may be accomplished by observing 

 whether there are two or four large hooks ; whether there be one 

 or two connecting portions, and by noticing their several forms 

 and relations to one another ; and whether, again, there are hook- 



* Wedl, Prof. Dr. K. — Anatomische Beobachtungen ueber Trematoden, s. 34, 



efc seq., Wien, 1857. 



