No. 406.] AMERICAN FROGS. 815 
(American) frogs. In view of these differences there can, I 
think, be no question that the two forms are distinct species. 
From 2. clavigerum it differs in being smaller and less elon- 
gated and in having short limbs to the intestine, while in that 
form the limbs of the intestine reach nearly to the posterior 
end of the body. 
It is readily distinguished from 2. confusum by the fact that 
the latter form has the testes far forward, alongside of the 
pharynx. The resemblances and differences of these four 
forms may be best shown perhaps by the tabular statement 
on the opposite page of their chief characteristics. 
I have collected about fifty specimens of D. arcanum, all 
from frogs dissected in Massachusetts. I have not found them 
in western frogs. No record was kept of the species of frogs 
from which specimens were taken, and I have, therefore, no 
means of judging whether it occurs in all the different species 
or only in particular ones. The specimens collected were taken 
from frogs used for laboratory dissection, the greater number 
being the larger common species, except the bullfrog (R. cates- 
biana). 
I had hoped to supplement these observations, made mostly 
several years ago and in large part upon preserved specimens, 
by the study of other living worms; but, as such specimens are 
not to be obtained in Minnesota, it seems best to publish such 
notes as I have without further waiting. 
UNIVERSITY OF MINNESOTA, 
July 17, 1900. 
