aV THE STRUCTURE OF CLINOSTOMUM MARGI- 

 NATUM, A TREMATODE PARASITE OF THE 

 FROG, BASS AND HERON 



HENRY LESLIE OSBORN 



Froyn the Biological Laboratory of Hamline University, St. Paul, Minnesota 



SEVENTEEN FIGURES 



PREFATORY NOTE 



In a previous article an account was given of the distribution 

 in this country and Canada of Chnostomum marginatum to- 

 gether with some notes on its habits. A short time after the pub- 

 Ucation of that article (Osborn, '11) Professor Linton informed 

 me that he had recently found specimens of Clinostomum mar- 

 ginatum in brook trout which were taken from Alder Lake, a 

 private preserve in the Catskill Mountains in New York. The 

 conditions under which the trout live are well described by 

 Linton ('10). "It is a lake of forty acres in the heart of the moun- 

 tains. The owner maintains a well equipped hatchery on the 

 stream below the outlet and allows no other fish than trout in 

 the lake." It is thus clear that the infection takes place in the 

 lake, or, in other words, that the first stages of this worm and 

 its primary host are to be found there. The lake is visited by 

 fish-eating birds and thus we can readily account for the intro- 

 duction of the parasite. As pointed out in my previous article, 

 we possess no information as to the early stages in the life history 

 of Clinostomum. We do not know its first host nor anything 

 about its development. It is evident from the facts now known 

 as to the occurrence of the parasite at Alder Lake that the infec- 

 tion must come from some form living in that lake, very likely 

 some invertebrate serving as food to the trout. Occurrence in 

 a small lake narrows down the problem of discovering this missing 



189 



JOURNAL OP MORPHOLOGY, VOL^23, NO. 2 

 JUNE, 1912 



