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found, in Ontario Canada, two specimens of a trematode, encysted in 
the liver of Rana catesbiana, which he identified with the D. medians 
of Olsson. In October of the same year Nickerson published an 
account of the structure of a fluke, which he had frequently found in 
Massachusetts, encysted in the wall of the duodenum at the pylorus of 
various species of the genus Rana, but not of the species catesbiana. 
Nickerson recognized this form as new and described it under the 
name of Distomum arcanum. He thus contributed a new member to 
the family Pleurogenetinae. In a paper written five years later Stafford 
recognized the identity of the Ontario form with Nickerson’s species 
arcanum. He separated this species from the rest of the family because 
of »its generative opening being situated on the ventral surface midway 
between the left coecum and the margin«. Nickerson in his account 
had made the error of locating the generative opening on the ventral 
surface whereas it is dorsal in location and Stafford followed in the 
same mistake. 
There have been only two localities recorded for this form until in. 
1909 it was found by the writer in frogs which had been obtained in 
the region about Saint Paul. In this instance the worms were encysted 
on the dorsal side of the neck of the urinary bladder of a female frog 
measuring 96 mm. The details of this case are shown in figure 1. On 
folding back the anterior part of the bladder so as to display its dorsal 
surface a large oval sack was found. This was anabnormal outgrowth of 
the neck of the bladder, which extended forward to and adhered slightly 
with the duodenum. This sack measured 13 X 9mm. On being opened, 
it was found to be very thick walled, and filled and distended with a 
fine-grained whitish material, scattered through which were limited num- 
bers of the eggs of L. arcanum. There were no flukes in the cavity of 
the sack and there was no open communication from the sack to the 
bladder. - There was no positive evidence to indicate that the flukes 
were responsible for the presence of the sacks, though that seemed likely. 
The four cysts already mentioned were examined. They were entirely 
closed. Hach one contained a single specimen of L. arcanum. 
This species has been met twice subsequently in Minnesota frogs, 
from the neighborhood of Saint Paul. In May 1911 four individuals 
were found in the urinary bladder of a female specimen of Rana pipiens 
measuring 58mm. Hach one of the flukes was enclosed in a thin-walled 
cyst, the four cysts being free in the right horn of the bladder. As they 
were dark colored and distended the organ considerably they were quite 
conspicuous objects. Still another occurrence of the worm was observed 
in July 1911, this time in a female frog of 74 mm. The worms were 
encysted at the pylorus, apparently in much the same way as those 
