272 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
I 
3. Carcharhinus obscurus, Dusky Shark. 
(1) July 18; one; a small skate the only identifiable stomach contents. All the parasites found 
in this shark were cestodes, as follows : 
Anthobothrium laciniatum (Cestode Parasites of Fishes, p.439), numerous, spiral valve. 
Orygmatobothrium angustum (Cestode Parasites of Fishes, p. 443), numerous, spiral valve. 
Phoreiobothrium lasiwm (Cestode Parasites of Fishes, p. 447), numerous, spiral valve. 
Tetrarhynchus bisulcatus (Cestode Parasites of Fishes, p. 452), very numerous, pylorus. 
The pyloric portion of the stomach, which was about 46 cm. in length, was crowded throughout 
its length with Tetrarhynchus bisulcatus, of which there were approximately 300 specimens. These 
worms had their heads deeply embedded in the mucous membrane of the pylorus, several of them 
often being attached at the same point, the strobiles hanging in a festoon from a common pit in the 
pylorus wall. The mucous membrane, especially in the vicinity of the pits, was in a highly inflamed 
condition. It is quite conceivable that these parasites might occasion the death of their host by 
giving rise to such irritation as to occlude the passage by the consequent swelling of the mucous 
membrane and underlying tissues. In several places the strobiles themselves were so numerous as to 
offer serious resistance to the passage of food. These specimens were larger than usual, many of them 
when straightened, while living, measuring as much as 40 cm. 
It would appear from a consideration of the occurrence of these parasites in this case that the 
most defective part of the alimentary canal of the shark is not the spiral valve but the slender pylorus. 
This is borne out also in the case of the tiger shark. The three species of cestodes found in the spiral 
valve, while occurring in great numbers and attaching themselves to the mucous membrane, are 
small and do not occasion much irritation by their presence. 
(2) July 19; one, stomach contained a partly digested squeteague. The shark had been confined 
in the large pool for a week or more. No parasites in stomach or pylorus. In the spiral valve the 
following cestodes were found : 
Anthobothrium laciniatum, few. 
Discocephalum pileatum (Entozoa of Marine Fishes of New England, ii, pp. 781-787, pi. X, figs. 
1-7) 12, large and small. 
Orgymatobothrium angustum, few. 
The largest specimen of Discocephalum was over 40 cm. in length and 7 mm. in breadth. The 
last segments were almost square and nearly 4 mm. long. The disk-like head, resembling a mush- 
room anchor, was firmly embedded in the submucous coat in each case, and had to be dissected out 
before it could be removed. 
One of the heads was stained in borax carmine and sectioned. Nerve cells were distinguished 
in the axis of the head in the basal part of the disk and also in the corrugated portion behind the 
head. Fibers from the axis continuous with those iu the anterior part of the strobile diverge at the 
base of the disk and make up a large part of that organ. These fibers are most abundant and con- 
spicuous in the basal part of the disk, as are also the vessels of the water- vascular system, which 
appear, indeed, in the anterior part of the disk, but are there few. 
(3) July 27; one, young; remains of young mackerel iu stomach. Two species of cestodes were 
found in the spiral valve. 
Anthobothrium laciniatum, 19, both long and short necked varieties. 
Phoreiobothrium lasium, 6, largest 32 mm. 
(4) August 9; one; stomach contained partly digested fish of good size, probably a squeteague. 
Unfortunately only the stomach, including the pylorus of this specimen, whs examined, the spiral 
valve having been taken by another for use as a specimen. 
At. the lower end of the stomach proper, not yet in the constricted pylorus, were four specimens 
representing three species, which, in view of the stomach contents, are of special interest. 
Echeneibothrmm (?) larva, 1, active. 
Tetrarhynchus bisulcatus , 2, scolices only, active. 
Nematode, immature, 1, partly digested. 
The two cestodes are just such as are found in the squeteague, the former in the cystic duct and 
intestine; the other ( Tetrarhynchus ) encysted in the submucosa of the stomach. In the larva there 
was a faint indication of two red pigment spots back of the bothria. The nematode appeared to be 
identical with immature forms collected from a squeteague on August 5. The condition of these 
