40 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



in aquaria, and I have met with it in great numbers on the skin of these 

 fishes in the adult state over the whole body of the fish and looking like 

 very minute leeches. They are said to especially attack the gills of 

 Cyprinoids, such as Cyprinus, Carassius, PhoxinKS, and Acerina in Eu- 

 rope. Here in the United States I have seen thousands on a single gold- 

 fish creeping over every part of the body, and thej- cannot therefore 

 fail to be very injurious. This type is said to be viviparous, and to 

 reproduce itself by internal gemmation parthenogenetically ; a second 

 generation appears within the first and even a third within the second 

 before the Gyrodactylus is born. It is very small; has a large terminal 

 sucking disk bearing a circlet of powerful hooks, with two long curved 

 median spines more developed than any of the other parts of the arma- 

 ture of the sucking disk. These parasites are doubtless often trans- 

 ported from one part of the country to another with gold-fish for orna- 

 mental purposes, and in this way uninfested fish probably often be- 

 come infested by being brought into contact with others which harbor 

 the parasite. 



Another genns of these parasites, Bucephalus^ is said to infest the Eu- 

 ropean oyster, Ostrea edulis, and passes into the encysted state in a fish 

 which serves as food for a larger fish, Belone vulgaris, in the intestine 

 of which the adult of the same worm, a species of Gastrostomum occurs. 

 The American oyster, Ostrea virginica, is said to be infested by Buceph- 

 alus cuculus, Macrady. This should deter epicures from indulging too 

 freely in raw oysters, in the ovaries of which it is said to occur, though 

 it is probably a rare parasite, since in examining the soft parts of great 

 numbers of oysters, it has never been my good fortune to meet with it. 



The foregoing data supply us with the means of accounting for the 

 manner in which the cysts found their way into the skin of the Cuuners. 

 It is probable that some mollusks inhabiting the waters in great num- 

 bers where the fish were taken were badly infested with the agamic 

 nurses from which the tadpole like larvae escaped in great numbers, which 

 then bored into the skin of the Cunners. But in order that the latter 

 could be as badly infested as are the Wood's Holland Cape Breton si)ec- 

 imens, the free-swimming, Cercaria-stage of the parasite must have lit- 

 erally swarmed in the surrounding waters, if each of the thousands of 

 cysts found on a single Gunner represents a Cercaria, as must be the 

 case. I have before me sixteen specimens of infested Cunners from 

 Cape Breton, the smallest 3J inches, the largest 7 inches long, while the 

 single specimen from Wood's Holl measures nearly 11 inches in length. 

 Even the smallest of these specimens harbor not far short of a thousand en- 

 cysted parasites, and some of the largest would i)robably by actual count 

 be found to have five tim es as many imbedded in the skin. From thi& 

 circumstance it is fair to infer that the surrounding water at the time 

 the fish became infested must have been swarming full or literally alive 

 with free-swimming Cercarice, which bored into every exposed part of 

 the skin o«f the fish, as our examination of the specimens has shown. 



