LIFE HISTORY OF A TROUT PARASITE. 
341 
serous membrane. It was translucent white, bluish with transmitted light, 20 milli- 
meters in length and 1.75 millimeters in breadth. 
(4) Four trout examined ; a few cysts in each, and a free larva 31 millimeters in 
jength, yellowish white ; one cyst, 9 millimeters by 4.5 millimeters in the two principal 
diameters ; when opened, liberated an active larva 15 millimeters in length and 1 mil- 
limeter in breadth. Along with larva in the cyst was a considerable amount of milky- 
white nutrient material. Larvae were seen to make their escape from cysts that had 
been left lying for an hour or two in water. 
Mem. — The Dibothrium cysts are found in the majority of the trout, but usually 
not in great numbers. Often the development appears to have been arrested, and the 
cyst degenerates into a calcareous or waxy calculus. 
(5) July 29. — Six trout examined; only one found with cysts in abdominal cavity. 
(6) July 30. — One trout examined ; a few cysts among pyloric coeca. 
YELLOWSTONE LAKE.. 
(7) August 1. — Five trout examined; taken in trammel-net near camp on west 
arm of lake near Lake-shore Geyser Basin ; all with cysts, two with many, one with 
worms in flesh, three with worms escaped from cysts, and one with worm under peri- 
toneum, not yet in flesh. Of these five trout the first was a male about 35 centi- 
meters in length, few cysts ; the second a female, same size, about thirty small cysts, 
the largest 3 by 6 millimeters, on pyloric coeca, some of the cysts with the larvae 
escaping, some yellowish and waxy, two cysts on ovary, the largest 12.5 millimeters 
in length, cyst about size of a small pea in the liver ; the third, a male, same size, 
several cysts on pyloric coeca, one laiva about 5 centimeters in length nearly free from 
its cyst ; the fourth, a male, same size, two or three cysts on pyloric coeca, one cyst 
under peritoneum, not in flesh ; the fifth, a male, a little larger than the others, about 
thirty-six cysts on the pyloric coeca, one larva 38 millimeters long outside of peri- 
cardial cavity, two cysts in testes, one larva in flesh a short distance back of right 
ventral fin 5 centimeters in length, coiled irregularly, flesh surrounding it inflamed 
and sore, pit made from peritoneal side, two others under peritoneum of air-bladder, 
surrounded by inflamed tissue, with apparently a good deal of lymph exuded. One 
of the larvae taken from the muscles of the latter specimen, after lying in water for 
two hours, measured 24 centimeters in length, and an hour or two later 34 centimeters 
in length ; greatest breadth 2.5 millimeters. 
(8) August 2. — One trout caught with hook and line near warm water of geyser 
basin, a spent female; two hundred and twenty cysts of various sizes on pyloric caeca; 
one larva in flesh, beneath peritoneum, on left side back of pectoral fin; one on left side 
back of gill slit ; two on right side back of gill slit ; one in liver ; a few cysts scattered 
along intestine and ovary; fish in poor condition. Five trout examined, caught with 
hook and line a short distance from entrance of warm water ; few cysts, no flesh worms. 
Five others from near warm water, caught in trammel net, more or less infested with 
cysts; one large larva in intestinal wall of one of the fish, intestine adherent to body 
wall and larva beginning to penetrate the latter; one larva in flesh above the lateral 
line, near the dorsal fin ; four others from same lot ; several cysts, none in flesh. Nine 
others, caught with hook some distance from warm water; no worms in flesh; a few 
cysts on intestines and in ovaries of a female. 
