FLESH PARASITES OF MARINE FOOD FISHES. 1 1 99 



and alewives, but, so far as my researches have gone, the flesh parasites appear 

 to be confined to the young fish. It seems probable that the badly infected 

 young do not reach maturity. Our knowledge of the life cycle of the sporozoa 

 is very fragmentary, and it is perhaps better to expend our energies in the accu- 

 mulation of knowledge, even if it must consist largely of apparently unconnected 

 facts, than to attempt to explain what further investigation may show in a 

 clear light. 



NEMATODA. 



While immature roundworms are very common on the viscera of fish, 

 they are, fortunately from our point of view, of exceedingly rare occurrence in 

 the flesh of marine fish. I have not found them in the flesh of any of the fishes 

 which are strictly food fish at Woods Hole, Beaufort, or Tortugas. In Ber- 

 muda I found numerous roundworms (Ichthyonerna globiceps) in the flesh of a 

 gar (Tylosurus acus) . These were colored blood-red and lay in tangled clusters 

 in the flesh, most abundant near the backbone. They bore a close resemblance 

 to blood vessels. I have occasionally found this species, or a species near it, 

 in the ovaries of some of our food fishes. If these were of common occurrence 

 the fact would be somewhat disturbing. The worms are long and thread-like, 

 often growing to the length of several inches. They are, moreover, crowded 

 either with ova or, in most cases, with the young. The latter are very minute, 

 but very active, and are in vast numbers. What would be the result if eaten 

 in insufficiently cooked food is not known. If, like the dread Trichina, they 

 can resist the digestive juices of the human stomach, they might easily pene- 

 trate the mucous membrane and, carried by the blood, finally lodge in congenial 

 tissues of the body, to become encysted, provided the body is able to stand the 

 inflammation produced by the invasion. 



Nematodes are very resistant to digestive fluids and are much more to be 

 feared than either trematodes or cestodes. In addition, they are nearer the 

 popular conception of the word worm than representatives of other orders of 

 the helminths. It is, therefore, a satisfaction to state that the probability of 

 consuming nematodes along with our fish food is very slight, indeed, and in no 

 way to be compared with the like probability in the eating of pork. 



TREMATODA. 



While this order of flat worms has a very large representation among the 

 species of entozoa inhabiting fish, their occurrence in the flesh of marine fish is 

 extremely rare, so much so that the few cases which I have recorded must be 

 regarded as accidental. The only cases where members of this order are at all 

 likely to enter our alimentary canals along with our fish food will be as skin 

 parasites. Many fish, especially tautog, cunner, and, to a lesser degree, flounders. 



