OBSERVATIONS CONCERNING FISH-PARASITES. 107 



not infrequently work them positive harm aud lessen their chances, by some not 

 inconsiderable increment, of long life with all that that means to the species in the life 

 race. My check-list shows that I have examined this fish nine times in the course of 

 several successive years, and have obtained this particular echinorhynchus in all but 

 one lot. 



Almost every specimen of such common food-fish as Cynoscion, Pomatomus, Roccus, 

 etc., that I have examined, has been found to harbor a greater or less number of larval 

 forms, of which the genera Rhynchobotlwium, Tetrarhynchus, and Syndesmobothrium 

 are most common. Frequently one will be found which is so badly parasitized that 

 it is quite evident that the fish is obliged to expend a considerable stock of its own 

 vitality to nourish its uninvited guests. 



In the autumn of 1889 Dr. David Starr Jordan found an interesting case of par- 

 asitism in some young suckers (Catostomus ardens) which he had collected in Witch 

 Creek, a small stream which flows into Heart Lake, in the Yellowstone National Park. 

 Specimens of these parasites were sent to me for identification. They proved to be 

 a species of ligula, probably identical with the European Ligula simplicissima Rud., 

 which is found in the abdominal cavity of the tench. On account of its larval condi- 

 tion, in which it possesses few distinctive characters, I described it under the name 

 Ligula catostomi. These parasites grow to a very large size when compared with 

 the fish which harbors them, often filling the abdominal cavity to such a degree as 

 to give to the fish a deceptively plump appearance. The largest specimen in Dr. 

 Jordan's collection measured, in alcohol, ''8.5 centimeters in length, 8 millimeters 

 in breadth at the anterior end, 11 millimeters at a distance of 7 millimeters from the 

 anterior end, and 1.5 millimeters near the posterior end. The thickness throughout was 

 about 2 millimeters. The weight of one fish was 9.1 grams, that of its three parasites 

 2.5 grams, or 27£ per cent the weight of the host. If a man weighing 180 pounds 

 were afflicted with tapeworms to a similar degree, he would be carrying about with 

 him 50 pounds of parasitic impedimenta. 



In the summer of 1890 I collected specimens from the same locality. A specimen 

 obtained from a fish 19 centimeters in length, measured while living 39.5 centimeters 

 in length and 15 millimeters in breadth at the anterior end. Another fish, 15 centi- 

 meters in length, harbored four parasites, 12, 13, 13, and 20 centimeters long, respec- 

 tively, or 58 centimeters aggregate. Another fish, 10 centimeters long, was infested 

 with a single parasite which was 39 centimeters in length. 



These parasites were found invariably free in the body cavity. Dr. Jordan's collec- 

 tions were made in October aud mine in July of the following year. Donnadieu has 

 found that this parasite most frequently attains its maximum development at the end 

 of two years. It is probable, therefore, that Dr. Jordan and I collected from the same 

 generation. Since these parasites, in this stage of their existence, develop, not by 

 levying a toll on the food of their host, after the manner of intestinal parasites, but 

 directly by the absorption of the serous fluid of their host, it is quite evident that 

 they work a positive and direct injury. Since, however, they lie quietly in the body 

 cavity of the fish and possess no hard parts to cause irritation, they work their mis- 

 chief simply by the passive abstraction of the nutritive juices of their host, and by 

 crowding the viscera into confined spaces and unnatural positions. The worms, in 

 almost every case, had attained such a size that they far exceeded in bulk the entire 

 viscera of their host. 



