Diseases of Fishes 349 



found in the abdominal cavity of the tench. On account of 

 its larval condition in which it possesses few distinctive char- 

 acters, 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 the fish a deceptively plump appear- 

 ance. The largest specimen in Dr. Jordan's collection meas- 

 ured, in alcohol, 2 8.5 centimeters in length, 8 millimeters in 

 breadth at the anterior end, 1 1 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 mil- 

 limeters. The weight of one fish was 9.1 grams, that of its 

 three parasites 2.5 grams, or 27 J per cent, the weight of the 

 host. If a man weighing 180 pounds were afflicted with tape- 

 worms 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 centimeters in length harbored four parasites, 12, 13, 

 13, and 20 centimeters long, respectively, or 58 centimeters 

 aggregate. Another fish 10 centimeters long was infested 

 with a single parasite which was 39 centimeters in length. 



' ' These parasites were f oimd invariably free in the body 

 cavity Dr Jordan's collections were made in October and 

 mine in July of the following year. Donnadieu has found that 

 this parasite most frequently attains its maximum develop- 

 ment 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 mischief 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 



