234 RESEARCH SEMINAR. 



An account of the varying degrees of infection, from that of 

 the presence, in the visceral mass, of a simple unbranched spor- 

 ocyst, to the almost complete replacement of the gonads and 

 liver by the long germ tubes, or branches of the sporocyst, was 

 first given. 



The first experiments described were conducted for the purpose 

 of determining whether infection might spread directly from one 

 oyster to another. Five experiments covering about one year, 

 were mentioned. 



In the second experiments conducted, an attempt was made 

 to obtain the adult form by feeding infected oysters to fish which 

 were kept in aquaria. These experiments seemed to show con- 

 clusively that the host of the adult form of Bucephalus was not 

 necessarily an oyster-eating fish. 



While these experiments were being carried on, a search for 

 Gasterostojiiujn, to which Bucephalus, by reason of its structure, 

 would seem to be intimately related, was being made. The 

 animals and plants found in the regions in which infected oysters 

 occur, were thoroughly examined. 



Gastcrostoiiniin was ultimately found in abundance in the gar- 

 fish, Tylosnnis inarinus. 



After determining the food of the gar, collections of the vari- 

 ous fish and Crustacea included in this list were examined. 



In the viscera of the silverside, Menidia notata, specimens of 

 which had been found in the stomach of the gar, encysted forms, 

 little different in appearance from the cercariae present in the 

 oyster, were obtained. 



The final set of experiments consisted in feeding viscera of the 

 silverside to four species of fish, previous examinations having 

 shown that in these species Gasterostomum does not occur. 



These experiments showed that the encysted forms from the 

 silverside were able to resist the action of the digestive juices of 

 the fish to which they were fed and that they attached themselves 

 to the wall of the intestine of their new host and continued in 

 their development. 



The evidence afforded by these experiments and observations 

 showed that during its life history Gasterostoimnn, parasitic in 

 the digestive tract of Tylosnnis niariniis, passes its cercaria stage 



