NOTE ON DISTOMUM ARCANUM (N. SP.) IN 
AMERICAN FROGS. 
W. S. NICKERSON. 
In frogs used for laboratory dissection I have observed, in 
many cases, cysts forming considerable swellings just at the 
pylorus. These, when opened, are found to contain small dis- 
tomes, together with a mass of friable material, which under 
the microscope is seen to consist in part of eggs and in part of 
a finely granular stainable substance whose source I, have not 
determined. The worms, though closely resembling several 
species which inhabit the intestines of European frogs, seem 
nevertheless to be distinct from them morphologically, and have, 
I believe, not been mentioned heretofore. I shall describe them 
under the name Distomum arcanum, the specific name referring 
to their being concealed from view in the cyst. So far as 
observed, the cysts occur always, when present, just at the 
pylorus, where they form conspicuous rounded swellings, about 
three millimeters in diameter. In extreme cases of infection 
as many as four or five of these may be present in the same 
frog. Two worms are usually present in a cyst. The wall of 
the cyst is composed of fibrous tissue and smooth muscle, which 
completely surround and enclose the contents. Several series 
of sections of cysts and contents have failed to show any indi- 
cation of a connection between the cavity of the cyst and the 
lumen of the intestine. The accumulation of so large a mass 
of eggs and other material within the cyst tends further to dis- 
prove the existence of an opening from the cyst. The sexually 
mature worms have been completely imprisoned by their host. 
The preserved specimens are small, stout, ovoidal, or sphe- 
roidal worms, the largest measuring 274 X 134 mm., and the 
average size being about 134 X 14% mm. The rather small 
Suckers are of nearly equal size, the oral being slightly larger 
than the ventral The latter, which is rather feebly developed, 
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