186 Wisconsin Academy of Sciences, Arts, and Letters. 
rock bass 73, pumpkinseed 71, sucker 68, black bullhead 66, tad¬ 
pole cat 64, wall-eyed pike 61, speckled bullhead 60, long-billed 
gar 56, bluegill 55, yellow bullhead 55, all species of ciscoes 54, 
largemouth black bass 45, pickerel 42, carp 40, buffalo (Ictiohus 
cyprinella) 36, log perch 35, blunt-nosed minnow 32, top minnow 
32, yellow perch 31, shiner (Notropis heterodon) 30, Johnny darter 
30, black crappie 27, shiner (Notropis atherinoides) 14, bream 11, 
shiner (Notropis hudsonius) 11. 
In general the fishes that frequent vegetation show the highest 
infection with parasites, those that frequent the bottom and open 
water are intermediate, and the small fishes that live in shallow 
water have fewest parasites. Doubtless many factors influence 
the prevalence of fish parasites, and much is yet to be learned 
before general laws that will enable one to predict the degree of 
infection that will be probable in a particular locality are for¬ 
mulated. 
There are many ways in which parasites may infect fishes. The 
most important means of infection are: (1) food, (2) the active 
migration of the parasite to its host, (3) and accidental contami¬ 
nation from bottom mud, vegetation, or other material. Van 
Cleave (1920) and Mrazek (1891) have found parasites encysted 
in amphipods. The observations described in this paper show that 
the fishes in Lake Michigan that feed largely on amphipods are 
heavily infected with the parasites these crustaceans are known 
to carry. Several types of parasites are found encysted in fishes 
and fish-eaters often have a heavy infection. Hausmann (1897) 
believed that fishes acquired parasites chiefly through their food, 
and he was doubtless right, as intestinal parasites are most abund¬ 
ant. In general the fishes that eat the greatest variety of food 
have the most parasites, but there are some notable exceptions to 
this. The dogfish, wall-eyed pike, and gar, for example, subsist 
largely on fishes (Pearse 1918) and are heavily infected. 
Little is known of the active migration of fish parasites to their 
hosts. The distribution of the cuticular cysts of Diplostomum in¬ 
dicates that infection may occur in such a way. Faust (1918) 
notes that Bunodera has been known to wander out of dead fishes. 
Perhaps parasites may infect a second host after leaving the first. 
The acquiring of parasites from the accidental ingestion of 
eggs or other stages may be characteristic of certain parasites that 
are erratic in their occurrence—like intestinal nematodes. 
