FLESH PARASITES OF MARINE FOOD FISHES. I203 



This parasite is a cestode, described first from adult forms found in the 

 spiral valve of the hammerhead shark (Sphyrna zygcena)." In the butterfish 

 it is found, sometimes in enormous numbers, in the flesh. The favorite resting 

 place of these cysts is between the vertebral spines on the ventral side of the back- 

 bone, but they are often almost equally abundant between the vertebral spines 

 on the dorsal side of the backbone, and scattered generally through the muscles 

 of the body, for the most part in a dorsoventral median plane. The cysts are 

 small, usually i millimeter or less in greatest diameter, oval in shape, and 

 present the appearance of small fish-roe. In the young fish they are translucent 

 white, which becomes tinged with yellow in the larger fish. Each cyst, when 

 crushed, liberates a characteristic cestode nurse (plerocercus or blastocyst) in 

 which is the scolex or head of the tapeworm. In all the cysts that I have 

 studied this season, even those from the smallest fish, I have not failed to find a 

 well-formed scolex bearing the characteristic marks by which the species may 

 be recognized. In former years the smaller fish were found to be much less 

 infected than the older fish and many were found in which no cysts were seen. 

 Also in former years cysts were found in some of the smaller fish which contained 

 scoleces in which the characteristic hooks on the proboscides and the pits on the 

 bothria were not yet developed. In the season of 1908 even the smaller fishes 

 were found to be largely infected. As they are recorded in the tables, the group- 

 ing into "cysts in enormous numbers," "very numerous," "numerous," etc., 

 is more or less arbitrary. It is to be hoped, however, that it will convey a fairly 

 correct picture of the actual condition. Of course the terms are to be under- 

 stood as of only relative significance. A small fish, for example, recorded as 

 having numerous cysts would contain a smaller actual number than would a 

 large fish similarly characterized. 



This case of parasitism of the individuals of a species which inhabits the 

 open sea is most exceptional. In a confined area, as in a small lake, or in excep- 

 tional conditions, such as obtain in as large a body of water as Yellowstone Lake, 

 a general prevalence of parasites can be accounted for.** But why should the 

 butterfish and its near relative, the harvestfish, be so excessively and universally 

 parasitized while other species of fish, though they inhabit the same waters and 

 feed on practically the same food, escape? That an occasional butterfish should 

 be found with these cysts in the flesh would not of itself be a thing remarkable. 

 That these cysts should even be present in very large numbers, even thousands, 

 as is often the case, is not inexplicable. That such an enormous percentage 

 should be affected, as is proved by the facts exhibited in the tabular statements 

 in this paper, is the really difficult matter to explain. 



o Linton, E. : Notes on entozoa of marine fishes of New England, with descriptions of several new 

 species. Report U. S. Fish Commission, 1887, p. 850-853, pi. xm, fig. 9-15; pi. xiv, fig. 1-4. 1891. 



b Linton, E-: On two species of larval Dibothria from the Yellowstone National Park. Bulletin 

 U. S. Fish Commission, vol. ix, p. 65-79, pl- xxiii-xxv; p. 337-358, pi. cxvii-cxix. 1891. 



