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THE AMERICAN NATURALIST [Vol. LIT 



believe that it is the larval stage of either some species 

 of Holostomum or Clinostomum. The latter is more nu- 

 merous in this lake; but the size and pigment strongly 

 suggest Holostomum, the adult appearance of which is 

 shown in the photomicrograph (Fig. 7). 



From the studies thus far made, I am inclined to think 

 that it takes one season for this larva to transform into 

 the adult worm. My reason for this conclusion is that 



there is so little difference between the several stages that 

 I have secured. 



In the hope of throwing some light upon the relation of 

 Trematodes to fish, the writer urged several years ago 

 that some " grubby" perch be placed in a separate tank 

 in one of the hatcheries and fed for one year to see what 

 happened, but the suggestion was rejected as not prac- 

 tical, although a number of specific experiments were out- 



