272 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



3. Carcharhinus obscurus, Dusky Shark. 



(1) July 18; one; ;i small skate the only identifiable stomach contents. All the parasites found 

 in this shark were cestodes, as follows: 



Anthoboihrium laciniatum (Cestode Parasites of Fishes, p. 439), numerous, spiral valve. 



Orygmatobothmutn angustum (Cestode Parasites of Fishes, p. 4 43), numerous, spiral valve. 



Phoreioboihrium lasium (Cestode Parasites of Fishes, p. 447), numerous, spiral valve. 



Tetrarhyndhus bisidcatus (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 bisulcatns, 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: 



Aiithobothnum laciniatum, few. 



Discoceplialnm pileatum (Entozoa of Marine Fishes of New England, n, pp. 781-787, pi. x, figs. 

 1-7) 12, large and small. 



Oryymalobothrium 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 in 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 in stomach. Two species of cestodes were 

 found in the spiral valve. 



Antliobotlirium 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, was 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. 



Echeneibothrium (?) 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 subiuucosa 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 



