Iigo BUI^IyETIN OF THE BUREAU OF FISHERIES. 



of parasites. To be sure, the number of hosts examined was small, and 

 this may account for the low total record. Two of these parasites, Azygia 

 sebago and Abothrium crassum, were found in every fish examined, and each of 

 six other parasites was found in two hosts. This may be compared with 

 Zschokke (1896, p. 824), who records the parasitic census of 10 salmon from the 

 North Sea. In these 10 fish were found 10 species of parasites. A trematode 

 and a cestode occurred each in 9 of the fish examined. The cestode was 

 Abothrium crassum, the same species as that found in every Sebago salmon; 

 the trematode was Distonium ocreatum, a purely marine form, and hence in 

 sharp contrast with the abundant trematode in the Sebago salmon, which is 

 a member of a characteristic fresh-water genus. This contrast, as well as 

 several other details commented on in the previous pages, seem to indicate 

 the fresh-water aspect of the parasitic fauna in the Sebago salmon. 



The conditions in the Sebago salmon are all the more striking when one 

 considers the forms which are not found among its parasites. Reverting first 

 to the trematodes, one notices that the only genus represented here, Azygia, 

 has been recorded from the Atlantic salmon in Europe only in a single case, 

 while here its representatives were found in every host examined. On the other 

 hand, Derogenes various, recorded from a good percentage of European salmon 

 in all localities, was not seen even once. The other distomes recorded by 

 European observers in various regions, and often as fairly frequent parasites 

 of the salmon, are entirely wanting in Sebago salmon. Azygia is the only 

 purely fresh-water distome found in European salmon; it is the only distome 

 found in the Sebago salmon. The other distomes recorded in European salmon 

 are purely marine species, or very largely so, but none of them occur in the 

 Sebago salmon. 



Among the cestodes conditions are identical. The common form, Abothrium 

 crassum, is confined to salmonids, without reference to their habitat, and is as 

 common in fresh- water species as in marine. On the other hand, those cestodes 

 which are typically marine, like Rhynchobothrium paleaceum, Scolex polymorphus, 

 and the several species of Tetrarhynchus, are absolutely wanting in the Sebago 

 salmon. The various cestode larvae are too little known to justify their con- 

 sideration in this connection. They are not referable, even indefinitely, to 

 either habitat. To this statement one must make two exceptions. Scolex 

 polymorphus, recorded from the salmon in Europe, is typically marine, occurring 

 in many sea fish, even though several species may be indicated under the single 

 name. On the other hand, the larva of Proteocephalus is equally typicallv 

 limnetic and it is recorded from the Sebago salmon only unless the single record 

 of Tcenia sp. for a larva from the salmon in the Tweed should be referred to 

 this form. In this group again it appears clear that the marine parasites of the 

 European salmon are wanting in the Sebago species, that the only cestodes 



