DIBOTIIKIA FROM YELLOWSTONE NATIONAL PARK. 
75 
YOUNG FORMS ENCYSTED IN ABDOMINAL CAVITY. 
[PI. XXVII, Figs. 1-4 and 6.] 
Larvie of this siiecies occur not only iu the abdominal walls, but also in cysts in the 
peritoneum of the stomach and intestines, particularly among the pyloric caeca, occa- 
sionally in the liver and spleen. Some of the cysts iu the trout submitted to me 
for examination contained embryos 4 centimeters and over in length. These were 
coiled up within the cyst in irregular folds, and in places the bodies were much con- 
stricted. One specimen whose average breadth was from 1 to 1.5 millimeters was 
constricted in one place to a diameter of .5 millimeter. This specimen, which was 
about 4 millimeters in length, was similar iu general outline to the larger specimens 
from the abdominal wall. Like them the body was crossed with fine transverse lines. 
Since these specimens frequently break at tlie narrow constrictions, many of the 
alcoholic specimens present a deceptive appearance, looking as if the larva might be 
a worm with a slender neck, such as may be seen in such worms as Dibothrium 
rugosum, whose anterior end is often fixed firmly in the tissues of its host and there 
degenerates into a slender core. Some of the cysts contained a waxy secretion with a 
calcareous mass at the center, but no parasite. These are evidently cases of arrested 
development where the tk^sues of the parasite have undergone degeneration. One cyst 
9 millimeters long and 5 millimeters broad after the connective tissue layers had been 
removed, when opened revealed an embryo which measured, approximately, 2.75 cen- 
timeters in length and was 1.5 millimeters wide at the widest point. The body was 
extremely irregular and had several constrictions. These were most pronounced near 
each extremity. On each side of a constriction the bodj^ swells out abruptly, produc 
ing an effect like that of a chain of small tubers. This phenomenon is doubtless due 
to the fact that much of the parenchyma of the body was in a plastic condition, and 
when the specimen was placed iu alcohol the result of the unequal contraction of dif- 
ferent parts of the body, together with its cramped and confined condition, was to im- 
press this characteristic outline on the parasite. A small specimen about 5 millimeters 
long was obtained from a cyst 7 millimeters in diameter. In the center of the cyst 
was an amber colored, rather hard mass, which effervesced slowly with dilute hydro- 
chloric acid. Another specimen, 8 millimeters long, folded once on itself, completely 
filled its cyst. This sijecimen was 2 millimeters broad, posterior end truncate, slightly 
emarginate, anterior end bluntly rounded. In some cases the embryos were embedded 
in the parenchytna of the cyst. In nearly every case the embryos were associated 
with a comparatively large mass of the original food-stuff. The cyst is evidently a 
nurse or blastocyst, with an investment of connective tissue, and the embryo has devel- 
oped by a process of budding within the blastocyst. The embryos are flask-shai)ed — 
larger at one end than the other — gradually tapering to the smaller end. Near the 
larger end they are distinctly shouldered. This character is not present when the 
extremity is invaginated. Beyond the shouldered part there is a somewhat narrowed 
prolongation with a slit on each lateral face. These slits appear to be rudimentary 
bothria. The cysts are, for the most part, irregularly globular or oval. One, however, 
was observed that was elongated; in the latter the contained embryo was straight. 
Anatomy . — One blastocyst containing an arcuate embryo curved around a ball of 
hardened parenchyma, and two embryos which had been liberated from their blasto- 
cysts were stained with borax carmine and cut into sections. 
