63 
On THE FisH Parasites, LeEPEOPHTHELRUS AND LERN@&A. 
By ANDREW Scort, 
Resident Fisheries Assistant at the Piel Hatchery. 
(With five Plates.) 
INTRODUCTION. 
There are comparatively few fishes that do not, at some 
period of their life history, prove on careful examination 
to be the host of at least one kind of parasite, either crus- 
tacean or worm. ‘The worm parasites are usually found 
infesting the alimentary canal (Nematodes and Cestodes), 
the gills and skin (Trematodes and Bdellodes), while 
Crustacean (Copepod) parasites are almost entirely con- 
fined to places in direct communication with the exterior, 
such as the skin itself, the fins, the mouth, the branchial 
chamber, attached to the gills and operculum, in the 
nostrils, and in the mucous canals. ‘They may even be 
found attached to the eye, as Lernwenicus spratte in the 
sprat (Clupea sprattus); and Lerneopoda elongata in the 
Greenland Shark* (Acanthorhinus carcharias), causing in 
the latter at any rate partial blindness; or burrowing into 
the abdominal cavity, as Penella évoceti in the flying 
fisht (Hvocetus volitans), till only the ends of the ovisacs 
are visible from the exterior. 
The Copepod fish parasites have attracted much atten- 
tion from Zoologists for a very long period, since the time 
when Aristotle, in his * Historia Animalium,” tells us 
that the tunny and the sword fish are tormented by a sort 
of worm which fastens itself under the fin. Many of 
* Mr. R. L. Ascroft, of Lytham, who visited Iceland on a ‘‘ steam liner,” 
fishing for halibut, &c., a year or two ago, says nearly all the sharks caught 
on the lines had these parasites in their eyes. 
+ One was exhibited at a meeting of the Liverpool Biol. Soc. in 1897, 
infested by two such parasites, recorded as P. blainvilli, which in turn 
were covered with a number of small Cirripedes.—Trans. L’pool Biol. Soc., 
vol. xi,, p. Xil. 
