LIFE HISTOKY OF A TROUT PARASITE. 
339 
condition of the specimens does not allow of their distinction from transverse fractures at irregular 
distances. No genital apertures could be detected at the sides or at the margins. Internal organs of 
any kind could not be seen, but the soft interior tissue of the body is filled with round corpuscles 
resembling in appearance starch-granules. These proved to be composed of carbonate of lime, as they 
were completely dissolved by acetic acid with the evolution of carbonic acid. From the shape of the 
head this tape-worm might appropriately be named Dibothrimi cordiceps. 
My attention was first called to this parasite in December, 1889, when specimens 
were sent me for identification by the U. S. Commissioner of Fish and Fisheries. 
These had been collected the previous autumn by Dr. Jordan, who published some 
account of them in his report on the fishes of the Yellowstone National Park.* These 
specimens, although in a good state of preservation, were in poor condition to show 
superficial characters owing to their crumpled and contorted condition. The bothria 
on the larger specimens were indistinguishable. The larva have the power of retract- 
ing the heatl, which character indeed seems to be retained to a certain degree in the 
larger specimens, and specimens on this account often do not exhibit the specific 
characters plainly. The report in which I published an account of this parasite, and 
which contains notes on the anatomy of this and another Dibothrium from the sucker 
{Catostomus ardens), gives, therefore, a rather meager description of the superficial 
anatomy of this worm. In my first report on this worm I suggested that some of the 
fish-eating birds inhabiting the lake would probably be discovered to be the final host 
of this parasite of the trout. When, therefore, the opportunity was afforded me of 
investigating the matter, I made an examination of such piscivorous birds as I could 
secure, with the result given below. 
III.- LARVAL STAGE. 
In the larval stage, Dibothrium cordiceps occurs either in cysts among or on the vis- 
cera of its host, the trout {Salmo myldss)) free, on or among the viscera; beneath the 
peritoneal lining of the abdominal cavity; or burrowing in the muscular tissue of the 
body-wall. 
The cysts, which are in reality blastocysts or nurses, within which the larvrn develop, 
are of various sizes. Some were found less than 1 millimeter in diameter, others were 
12 millimeters or more in the longer diameter. The smaller cysts are globular or sub- 
oval, the larger ones are oval. The smaller larvm up to a centimeter or more in length 
are lanceolate, flattish, tapering rather abruptly and uniformly to each end. The larger 
specimens are linear, increasing slightly in breadth posteriorly, with a blunt truncate 
or emarginate termination; the body is crossed by fine transverse wrinkles, closely 
crowded together, but in the longer specimens presenting the phenomenon of distinct 
segments one-half millimeter or more in length. In the living specimens the vascular 
system is quite evident. It consists of four longitudinal vessels, two near each margin, 
the smaller vessel of each pair being near the margin. Branches from each of the 
marginal vessels extend to the other and from each of the larger vessels to the other 
These branches also anastomose with each other by means of secondary branches 
(Pig. 11). The aquiferous vessels unite with two oval vessels at the posterior end, which 
is often emarginate, with a terminal pore at the emargination (Pig. 13). 
The head in the living worm is small and extremely variable, sometimes stretching 
out until it is linear and not more than one-fourth the ordinary diameter (Fig. 6); 
Bull U. S. F. C., 1889, pp. 41-63. 
