22O 



How to obtain it. 



deal in this chapter. There is one, 

 which attacks the young fish, known 

 as Iriclwdnia pediculus, a minute 

 creature just visible to the naked 

 eye. They are excellent free swim- 

 mers, and sometimes attach them- 



Fig. 41. Trichodnia 



selves to fry in large numbers, but 

 no special harm seems to follow from their presence, so far as we 

 have observed. When viewed under the microscope they make 

 beautiful objects and have some resemblance to a sea anemone. 

 They are easily killed by placing the fish in a saline bath. 



Another parasite that occurs on fry is probably one of the 

 Trematoda, which has the appearance of a small worm, and makes 

 another very beautiful and interesting object for microscopic 

 study. It is Gyrodaclylus elegans, and is possessed of fourteen 

 cat-like claws, with which it clings to its host. It is viviparous, 

 and on several occasions we have witnessed the birth of a young 

 one, which at once finds a suitable nidus on the fish, and 

 commences to feed. 



Fig. 42. Gyrodaciylus eleganS (enla'd). Fig. 43. Foo$o{Gf90dacty/vst/efettt*(.tn\a.'d). 



It has been suggested that there may be some connection 

 between these parasites and the fungoid growth (Saprolegaia) 

 which is often found on fish. After a most careful and extended 

 investigation, we could not, however, find facts to confirm the 

 slightest suggestion of any connection between the two. With 

 the aid of a powerful microscope we have watched them feeding 



