108 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



From the fact that the examples obtained were of comparatively the same age, it 

 may be justly inferred that the period of infection to which the fish are subjected must 

 be a short one. I did not discover the final host, but it is almost certain to be one or 

 more of the fish-eating species of birds which visit that region and presumably one 

 which, in its migrations, pays but a brief visit to this particular locality. This parasite 

 was found only in the young suckers which inhabit a warm tributary of Witch Creek. 

 They were not found in the large suckers of the lake. These young Gatostomi were 

 found in a single school, associated with the young of the chub (Leuciscus atrarius), 

 in a stream whose temperature was 95° F. near where it joined a cold mountain brook, 

 whose temperature was 46° F. We seined several hundred of these young suckers 

 and chubs, ranging in length from G to 19 centimeters. The larger suckers were nearly 

 all infested with these parasites, the smaller ones not so much, and the smallest scarcely 

 at all. Or, to give concrete examples: of 30 fish ranging in length from 14 to 19 cen- 

 timeters, only one or two were without parasites; of 45 specimens averaging about 

 10 centimeters in length, 15 were infested and 30 were not; of 65 specimens averaging 

 about 9 centimeters in length, 10 were infested and 55 were not; of 62 specimens less 

 than 9 centimeters in length, 2 were infested and 60 were not. None of the chubs 

 were infested with this parasite. 



The conditions under which these fish were found are worthy of passing notice. 

 The stream which they occupied flowed with rather sluggish current into a swift 

 mountain stream, which it met at almost right angles. The school of young chubs 

 and suckers showed no inclination to enter the cold water, even to escape the seine, 

 but would dart around the edge of the seine, in the narrow space between it and the 

 bank, in preference, apparently, to taking to the colder water. When not disturbed 

 by the seine they would swim up near to the line which marked the division between 

 the cold and the warm water, and seemed to be gazing with open mouth and eyes at 

 the trout which occasionally darted past in the cold stream. The trout appeared to 

 avoid the warm water, while the chubs and suckers appeared to avoid the cold water. 

 It may be that what the latter really avoided was the special preserve of the trout, 

 since large chubs and suckers are found in abundance in the lake, which is quite cold, a 

 temperature of 40° F. having been taken by us at a depth of 124 feet. 



Since the eggs of this parasite, after the analogy of closely related forms, in all 

 probability are discharged into the water from the final host and hatch out readily in 

 warm water, where they may live for a longer or shorter time as free-swimming, 

 planula-like forms, it will be observed that the sluggish current and high temperature 

 of the water in which these parasitized fish occur give rise to conditions which are 

 highly favorable to infection. 



It may be of passing interest to state here what I have recorded elsewhere, that 

 ligulse, probably specifically identical with L. eatostomi, form an article of food in 

 Italy, where they are sold in the markets under the name maccaroni piatti; also in 

 southern France, where they are less euphemistically but more truthfully called the 

 ver blanc. So far as my information goes, this diet of worms, like the historical episode 

 of that name, is strictly European. 



It is not necessary to prove cases of direct injury resulting from the presence 

 of parasites in order to make out a case against them. In the sharp competition 

 which nature forces on fishes in the ordinary struggle for existence, any factor which 

 imparts an increment either of strength or of weakness may be a very potent one, and 



