BY JAMES NELSON GOWANLOCH 127 



an example of these heavily infected hosts is studied it is found 

 to exhibit whitish areas on the fins, around the mouth and 

 around the eyes which areas, on microscopical examination, 

 resolve themselves into masses of closely adjacent, extremely 

 active Gyrodactylus . From two hundred and fifty to six hun- 

 dred of the parasites may be present on a single host. Fish 

 suffering from infection to this extent can be recognized easily 

 even on a hasty macroscopic examination since they present 

 a characteristic picture of anaemia. 



The Gyrodactylus studied does not accord with any of the 

 available specific descriptions and the determination or morpho- 

 logical description of the species will therefore be left to form the 

 subject of a subsequent account. On the writer's return to 

 Halifax Fundulus collected from various marshes within thirty 

 miles of Halifax were searched and were found to be frequently 

 and sometimes heavily infected with a Gyrodactylus evidently 

 identical with the species noted in the Bay of Fundy. 



Although not noted on any specimens of Sticklebacks 

 (fi aster osteus) collected, Gyrodactylus was found to thrive on this 

 host whenever Gasterosieus was placed in aquaria with infected 

 Fundulus. Such parasitized Gasterosieus showed even more 

 markedly than Fundulus the severe effects produced by the 

 trematodes and almost without exception died. The flounder 

 Pseudopleuronectes americanus proved to be immune to infection 

 even when optimal conditions for the migration of the parasites 

 to this host were provided. Careful examination of Pseudo- 

 pleuronectes that had been confined with Fundulus carrying 

 thousands of the parasites failed to show any infection and, 

 furthermore, isolation of the flounders with numerous de- 

 tached and hungry Gyrodactylus did not bring about parasitiza- 

 tion of this fish. 



An attempt was made to apply standard blood-counting 

 methods to the more severely affected Fundulus in order to gain 

 some exact measure of their abnormality but this was without 

 success since the blood invariably coagulated before it could be 

 diluted for spreading in the cell. The changes in blood were so 



