254 American Fisheries Society 



This season my time was occupied with the flesh parasite, 

 and I examined barely half a dozen of the cysts. In each 

 case I found the cyst to be exceedingly thick walled and the 

 contents degenerated to an indistinguishable granular mass. 



While the generic identity of these encysted trematodes 

 was not definitely ascertained, sufficient was revealed by 

 their structure to indicate that they belonged to that group 

 of trematodes whose adult stage is passed in the alimentary 

 canals of fish-eating birds. 



Hofer, in his Handbuch der Fischkrankheiten (Mun- 

 chen, 1904), discusses such cases as these under the caption, 

 "Die Diplostomumkrankheit or Diplostomiasis:" These 

 cysts have been recorded in a number of the European fresh 

 water fishes. Their usual situation is in the skin, although 

 at times they are found in the outer muscle layers beneath 

 the skin. The encysted worm represents the larva of a 

 trematode which is known under the name Diplostomum or 

 Holostomum cuticula. Hofer's description of the appear- 

 ance of these cysts in the skin of fishes is in practical agree- 

 ment with what I have observed in the fishes that I have 

 examined in this country. In the trout the presence of these 

 skin parasites was indicated by black specks which upon nar- 

 row scrutiny were seen to consist of an accumulation of 

 black pigment around a transparent cyst which is often 

 silver white and shining like a small crystalline lens. This 

 cyst usually lay just beneath the epidermis and projected 

 slightly so that the surface containing a number of them pre- 

 sented an embossed superficies which could be detected by 

 passing the hand lightly over it. 



While the life-history of these parasites of fresh-water 

 fish has not been worked out and must of necessity be con- 

 jectural, it may be said that there are the best of reasons 

 for believing that they are due to eggs which have been dis- 

 charged into the water along with the excreta of birds, and 

 no reasons for believing otherwise. Of course, it is possi- 

 ble that the cercari;e of distomes whose adult stages are 

 found in fishes and amphibians might become encysted in 



