162 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [456] 
ternal parasites were collected mainly by Dr. Edward Palmer, and will 
be of great interest when carefully studied and deseribed. As yet, noth- 
ing more than a casual examination of them has been made. These 
internal parasites were found in nearly all kinds of fishes, chiefly in the 
stomach and intestines, but also very frequently in the flesh, or among 
the abdominal viscera, or in the air-bladder, or even in the eyes, &e. 
The internal parasites were mostly worms, but these belong to four very 
distinct orders. 
Ist. The “ round-worms,” Nematodes. 
These are related to the round-worms so frequent in the intestines of 
children, and also to the notorious Trichina of man and the hog. One 
or more species are found in the intestine and stomach of nearly every 
kind of fish, and frequently, also, in the liver, peritoneum, eyes, and 
various other organs. One species, two or three inches long, is very fre- 
quently found coiled up spirally in the flesh of the cod. Another large 
species is frequently found in the flesh of the tom-cod, or frost-fish. 
Although these are not dangerous to man, they are very disagreeable 
when found in fish intended for food. 
A species belonging to this group is very frequently found in the body- 
cavity of one of our species of Sagitta (see page 440). 
2d. The flat-worms or “ flukes,” Trematodes. 
These are short, more or less broad, depressed worms, which are pro- 
vided with one, two, or more suckers, for adhering firmly to the mem- 
branes. They pass through very remarkable transformations, as do 
most of the other parasitic worms. Species belonging to this, group are 
common in the stomach, cesophagus, and intestine, and also eneysted or 
in follicles in the mouth, liver, peritoneum, and various other parts of 
the body. 
3d. The thorn-headed worms, Acanthocephala. 
These have an elongated roundish body, with a proboscis at the an- 
terior end, covered with hooks, or recurved spines. The proboscis and 
front end of the body can be withdrawn and thrust out at pleasure. 
Such worms are very common in the stomachs and intestines of fishes, 
and are, perhaps, the worst parasites that torment them. The young of 
these worms also occur quite frequently, encysted in the liver, peri- 
toneum, throat, mouth, and other organs. 
4th. The “ tape-worms,” or Cestodes. 
These are long flat worms, divided into many distinct segments, and 
are very frequently found in the intestines of most fishes. There are 
numerous species of them, ranging in size from less than an inch to 
many feet in length. 
Although parasitic worms are found in nearly all kinds of fishes, they 
are most frequent and in the greatest variety in the large and very vor- 
acious kinds, such as sharks, rays, the angler or goose-fish, salmon, blue 
fish, cod, haddock, Xe. 
Nor are other marine animals free from these internal parasites. Cer- 
