Pearse—The Parasites of Lake Fishes. 
189 
parasites than a restricted one. Ward (1910) has pointed out that 
“the parasitic fauna of any animal is primarily a function of its 
habitat”. The observations reported in this paper indicate that 
the fishes in comparatively barren lakes have an unusual number 
of visceral cysts and acanthocephalans—perhaps because they 
wander about more in search of food. Visceral cysts appear to be 
more abundant in deep water fishes than in those from shallow 
water. Linton (1910) found that marine fishes in shallow water 
had fewer parasites than those at greater depths. He believed 
this was because the former had less opportunity to wander about 
and become infected. In fresh-water the writer has found infection 
to be greater on the whole in shallow water—probably because 
there is a greater variety of habitats and secondary hosts there. 
The ecological factors that appear to be important in relation to 
parasitic infection have now been discussed. Perhaps only one 
thing has been made clear—that, “now we see through a glass 
darkly”. The writer makes no apology for this final conclusion. 
There is great need for more information in regard to the ecology 
of parasitism, not only among fishes but among all animals. It is 
hoped that this paper may help to interest fishermen, parasitolo¬ 
gists, geographers, and ecologists in the opportunities that are open 
for research on the parasites of fishes. The fisherman must in the 
future learn to increase his catch by the control of parasites. There 
are many undescribed species and life histories that await discov¬ 
ery by the parasitologist. The zoogeographer has unusual oppor¬ 
tunities for study—parasites depend on one or more hosts for their 
distribution and .are hence conservative in their migrations. The 
ecologist may disclose the most intricate and interesting relations 
to be found in nature. 
Bibliography 
Cooper, A. R. 1917. A morphological study of bothriocephalid cestodes 
from fishes. Jour. Parasitol. 4: 33-39. TJrbana. 
Fasten, N. 1913. The behavior of a parasitic copepod, Lernaeopoda ed- 
wardsii Olsson. Jour. An. Behavior, 3: 36-60. Cambridge. 
Faust, E. 0. 1918. Studies on American Stephanophialinae. Trans. Amer. 
Micro. Soc. 37: 183-198. Menasha. 
Goldberger, J. 1911. Some known and three new endoparasitic trematodes 
from American fresh-water fish. Bulletin XT. S. Hygienic Laboratory, 
No. 71: 7-35. Washington. 
Hausmann, L. 1897. Ueber Trematoden der Susswasserfische. Revue suisse 
die Zoologie, 6: 1-42, pi. 1. Geneva. 
