553 
the cyst proves that conclusively. If these were immature as are the 
forms of Clinostomum found quite commonly encysted in our frogs (Os- 
born 1911) we should account for encystment as an adaptation by 
means of which the parasite could reach a final host. On the other 
hand the imprisonment as in this case of both the parent and the eggs 
for an indefinite period of time is quite unintelligible. 
The form of body of L. arcanum is shown in figure 3, a view of 
the dorsal surface of a whole specimen in alcohol. The outline is heart- 
shaped, the oral sucker is located at the anterior end, the excretory pore 
lies in the indentation at the posterior end. The length 2,6 mm in this 
individual slightly exceeds the breadth which is 2,3 mm. In some, the 
two are 2 mm and thus about equal. In thickness the preserved worms 
measure about one third of their breadth. The drawing fig. 3 shows a 
decided deviation from a strict bilateral symmetry. The same is shown 
in Nickerson’s drawing, and is also found in several of my specimens. 
Since this asymmetry was not noticed in the living worms, I am inclined 
to attribute it to the action of reagents, the right side having shrunken 
more than the left where the heavy walled cirrus sack and metraterm 
are located. A careful study of the dorsal surface of several specimens 
showed very surely that the generative opening is located there, it being 
as shown in the figure midway between the margin of the body and the 
middle line. As this is at variance with the statements of Nickerson 
and Stafford on this point I was very careful indeed to verify my 
observations both by means of studies of the surface and by sections. 
In the vast majority of trematodes the opening lies upon the ventral 
surface and in a’ few it is lateral so that Loxogenes stands practically 
alone in regard to this matter. I have had the privilege of examining 
Nickerson’s sections and found that this opening is dorsal in his spe- 
cimens as well. There is thus no doubt at all upon this point and current 
statements must be revised. 
The ventral sucker occupies a position in the centre of the ventral 
surface. It is very small indeed, measuring only 0,025 mm. Its wall 
possesses the usual equipment of radial muscles of an organ of adhesion, 
but they are not developed so as to form a strong and powerful layer. 
The small size of the sucker suggests the possibility that it is rudimen- 
tary. A still more remarkable peculiarity of the ventral sucker and one 
entirely unique so far as I know in trematodes and one not hitherto recor- 
ded is the fact that the cuticle lining the cavity of the ventral sucker is 
clothed with heavy spines in the same way as that of the general exterior 
surface of the animal. Usually the spines cease at the margin of the ventral 
sucker but here they pass over the edge and clothe the entire interior 
cavity. These spines have the same size and form of those of the outer 
