IT.-A CONTRIBUTION TO THE LIFE HISTORY OF DIBOTHRIUM CORDICEPS 
LEIDY, A PARASITE INFESTINO THE TROUT OF 
YELLOWSTONE LAKE. 
BY EDWIN LINTON, PH. D. 
[With Plates cxvii-cxix.] 
I. — INTRODUCTION. 
In July and August, 1890, I was requested by the Hon. Marshall McDonald, 
U. S. Commissioner of Fish and Fisheries, to investigate this interesting parasite. 
My instructions were to join with Prof. S. A. Forbes, of Champaign, Illinois, in the 
field work of an expedition sent out by the U. S. Fish Commission for the purpose 
of investigating the life of the principal lakes and streams of the Yellowstone National 
Park, Wyoming, the special work assigned to me being to determine, if possible, the 
cause of the prevalence of parasites among the trout of Yellowstone Lake. 
I desire in this connection, to express my deep gratitude to Professor Forbes for 
the unabated interest which he took in my branch of the work and for the valuable 
hints and suggestions which I received from him. I should also be remiss if 1 did 
not express my personal obligations to Capt. F. A. Boutelle, D. S. Army, Suiierin- 
tendent of the Park, whose enthusiastic interest in the expedition and prompt assist- 
ance in many ways contributed very much to the successful conduct of the investi- 
gation. Mr. Elwood Hofer, our esteemed guide and friend, and Mr. F. D. Booth did 
much volunteer work which receives but inadequate compensation in this mention of 
their names. 
II. — BIBLIOGRAPHY. 
The literature relating to this parasite is confined for the most part to the reports 
of the IT. S. Geological Survey, under Dr. F. V. Hayden. 
The first mention of the worm that I find is in the Eeport on Montana and Adja- 
cent Territory for 1871, p. 97, where Dr. Hayden remarks as follows respecting the trout 
of Yellowstone Lake: 
We were able to discover but one species of fish in the lake, and that was trout, weighing from 2 to 
4 pounds each. Most of them are infested with a peculiar intestinal worm, which has been described by 
Dr. Leidy in a subsequent portion of this report as a new species, under the name Dibothrium cordiceps. 
337 
Bull. H. S. F. O. 89 22 
