220 How to obtain tt. 
deal in this chapter. There is one, 
which attacks the young fish, known 
as Zrichodnia pediculus, a minute 
creature just visible to the naked 
eye. They are excellent free swim- 
mers, and sometimes attach them- 
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 Gyrodactylus 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 z/dvs on the fish, and 
commences to feed. 
Fig. 41. Trichodnia pediculus (enlar’d). 
s 
c 
Ns 
~ \ 
Fig. 42. Gyrodactylus elegans (enla'd.) Fig. 43. Foot of Gvrodactylus elegans (enla'd). 
It has been suggested that there may be some connection 
between these parasites and the fungoid growth (Saprolegnia) 
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 
