THE CESTODE PARASITES OF THE PERCH. 

 GEORGE B. LA RUE. 



(Abstract.) 



The cestodes found in a considerable number of perch have been studied 

 and found to belong to three species. Of these, two infest the intestine of 

 the perch in relatively small numbers while the remaining species occurs in 

 the plerocercoid stage encysted in the viscera. These species and their occur- 

 rence may be summarized thus : 



Proteocephalus pearsei mihi. This species in both the juvenile and adult 

 form occurs in the intestine of perch in certain Wisconsin lakes, Douglas 

 Lake, and Hubbard Lake, Alcona County, Michigan. Adults were found in 

 11 perch out of 525 perch examined by the writer and others. This is 2.095 

 per cent. The juvenile form has been found in a larger number of hosts, 

 in the neighborhood of 11 per cent. 



Proteocephalus ambloplitis (Leidy). The plerocercoids of this species 

 occur encysted in the viscera of perch taken in lakes of Wisconsin, Michigan, 

 and Lake Erie. About 52 per cent of the perch are infested with this worm. 



Bothriocephalus cuspidatus (Cooper). This species has been found but 

 rarely in examinations of perch made by the writer and apparently not at all 

 by certain other investigators whose records have been available to the writer. 

 It has been recorded by Pearse in unpublished researches. In the writer's 

 examinations of perch this species was found but twice in 181 perch or a 

 little more than 1 per cent. 



From a study of the records the conclusion is drawn that the perch is 

 rarely parasitised by adult Proteocephalids. 



An explanation of this infrequent infestation is perhaps to be sought in 

 the varied diet of the perch. Since P. ambloplitis is found as plerocercoids 

 encysted in the viscera of the perch and since the perch is cannibalistic in its 

 habits one would be justified in looking for the adult of this worm in the 

 intestine of the perch; Thus far there are no records of its occurrence there. 

 The only explanation that can be offered for the present to account for the 

 non-occurrence of the adult in the perch is that the intestine of the perch 

 does not offer a proper habitat. As to the elements of that habitat which 

 are incompatible no explanation can be offered. 



University of Michigan, April 3, 1919. 



