Pearse—The Parasites of Lake Fishes, 
163 
of fishes are given in millimeters and do not include the tail fin. 
In the tables indicates less than 0.05. 
The work could never have been completed without the cheerful 
and excellent assistance rendered by Drs. George R. LaRue and 
H. J. Van Cleave, who identified Proteocephalidae and Acanthoce- 
phala, respectively. Others who deserve thanks for identifications 
are Dr. A. R. Cooper, tapeworms; Prof. H. S. Davis, Sporozoa; 
Dr. A. D. Howard, glochidia; Prof. J. P. Moore, leeches; and Prof. 
C. B. Wilson, copepods. Mr. Leslie Tasche assisted the writer 
in the field; Misses Henrietta Achtenberg and Marion E. Lamont, 
and Mr. J. C. Stucki mounted slides. 
Before all the factors which influence parasitism in fishes are 
known, if they ever are, parasitologists and ecologists will have to 
labor for several generations. This paper is, of course, only a 
beginning in the ecology of fish parasites and is concerned par¬ 
ticularly with certain Wisconsin lakes. 
PARASITES OP THE YELLOW PERCH 
From June, 1917, to May, 1918, the yellow perch from the deep 
waters of Lake Mendota were examined each month, except dur¬ 
ing December. During the summer and at intervals throughout 
the year perch from four other lakes on the Yahara River and 
from the shallow waters of Lake Mendota were also examined. 
The results of these studies are given in table 1. The parasites 
found in the perch in these lakes were as follows: 
Trematoda 
Diplostomum cuticola Van Nordmann 
This trematode was common, occurring in small cysts in the 
skin and fins, and sometimes on the gills. The cysts are easily 
seen on account of the black pigment that surrounds them and 
gives infected fishes a speckled appearance. Their distribution 
on the bodies of 335 perch from all the lakes studied averaged as 
follows: pectoral fins 1; pelvic fins 0.'9; anal fin 0.5; caudal fin 1.3; 
dorsal fins 1; anterior dorsal 0.4; posterior dorsal 0.5; gills +> 
opercles 1.3; ventrum 1.4; tail +; dorsum 2.4; sides 3.3. 
