212 American Fisheries Society 



cussion that this is at best an unstable foundation on which 

 to erect so important a structure. 



Our knowledge concerning the parasites of fresh-water 

 fish in North America is due first of all to the researches 

 of Dr. Joseph Leidy, a former distinguished physician and 

 naturalist of Philadelphia, who studied and recorded the oc- 

 currence of many species from American fish. It is said of 

 him that he was accustomed to visit regularly the local fish 

 market in search of parasites and the discovery of a new or 

 unusual form was a constant source of pleasure. His con- 

 tributions are numerous and valuable and his collection is 

 the most extensive yet on record in this country. It has been 

 listed by Stiles and Hassall (1894). 



The records of Verrill cover chiefly the parasites of ma- 

 rine fishes, and those of Linton are largely the same al- 

 though the latter has published several very important 

 papers on the parasites of fresh-water fishes; these are duly 

 entered and annotated in the appended bibliography. Ram- 

 sey Wright, Stiles and Hassall, Pratt, and Calkins have also 

 contributed important articles on this topic which, with 

 others of perhaps equal importance though more limited in 

 extent, are all included in the bibliography. From the stand- 

 point of the fish culturist the papers by Bean. Clark and 

 Marsh, among others, are deserving of especial mention. 

 Though embracing many titles the bibliography is probably 

 incomplete, even for the limited field it attempts to cover. 



The simplest of animal organisms are the single-celled 

 f( inns or Protozoa. Among these there are three groups, the 

 Sporozoa, the Flagellata, and the Ciliata, which furnish 

 disease-producing organisms harmful to the fishes. Un- 

 doubtedly the most important are the Sporozoa. which invoke 

 general diseases of frequent occurrence and serious in effect. 

 These organisms reproduce with extreme rapidity, giving 

 rise to a mass of individual parasites that invade the different 

 organs and tissues of the fish, bringing about changes in 

 various structures that ultimately endanger the life of 

 the host. 



