552 
described by Nickerson. Thedetails of this are shown in figure 2. Three 
cysts were present, two lay on the ventral surface of the mesentary, en- 
tirely free from the alimentary wall, in the angle between the stomach 
and the duodenum. The third was a growth upon the ventral wall of 
the duodenum at the pylorus. It was determined by means of a careful 
examination of the mucosa that the cyst cavity was entirely closed. The 
two smaller cysts measured 2,5 mm in diameter, the larger, 3,0 mm. 
The dark-colored bodies of the worms could be faintly seen through 
the walls of the cysts. The smaller ones contained each two worms and 
the larger one contained five. In the latter there was an accumulation of 
a creamy substance which was composed largely of eggs which had been 
Fig. 3. 
Fig. 1. Enlarged free hand drawing from bladder of frog after the anterior end had 
been drawn back so as to display the dorsal surface and at its neck the large sack 
and the four small cysts of D. arcanum. Drawn from an alcoholic preparation. 
Fig. 2. Enlarged view of the ventral aspect of a piece cut from the stomach, duo- 
denum and mesentery showing the position of the three cysts of D. arcanum. 
Fig. 3. View of the dorsal surface of L. arcanum with magnification of about 
10 diameters. 
discharged by the immured worms. Nickerson states that he had not 
found the wormin Minnesota. As the worms are quite conspicuous enough 
to readily attract attention and as the frog is used so extensively in bio- 
logical work we must conclude that it is very rare in this region. 
In view of the fact that the european forms related to this worm all 
live free in the alimentary canal, it is surprising to find that all the ameri- 
can forms thus far found are encysted either in the wall of the alimentary 
tube (Nickerson and Osborn) or else in the liver (Stafford) or uri- 
nary bladder (Osborn), organs connected with it. It is not at the present 
moment possible to account for the habit of encystment, which seems 
to be so characteristic of the American species. There is no room to 
doubt that these worms are fully matured. The discharge of eggs into 
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