554 
surface. It is quite impossible to find a physiological explanation for 
the presence of these spines in such a situation. It would seem that 
they would interfere with the action of the sucker as an organ for ad- 
hesion. The small size of the ventral sucker would indicate that it is 
of little use if any, possibly we may regard the organ as degenerating 
and reverting to the character of the general body wall. 
The internal organization of the Minnesota worms is shown in fi- 
gure 4, made from a drawing from a living specimen under slight com- 
pression, with some additions derived from serial sections. While the 
worms are too thick and dense for complete study alive and compressed, 
Fig. 4. View of L. arcanum as if it were a transparent object, seen from the dorsal 
surface ; based chiefly on studies from aliving compressed specimen with some points 
from serial sections added. Magnified about 20 diameters. 
many of the chief topographical points can be determined in that way. 
The testes ovary and vitellaria are lighter and more highly refractive 
than the surrounding organs. Many of the chief coils of the uterus can 
be followed. It was somewhat more complicated than the drawing. In 
the main the drawing corresponds with that of Nickerson apart from 
the position of the generative opening and excepting as to some minor 
details. 
The oral sucker lies in the extreme anterior end of the body, it is 
globular and measures about 0,02 mm. There is a much smaller pha- 
rynx immediately following and a very short gullet, in marked contrast 
with P. medians in which the gullet nearly equals the length of the 
coeca of the intestine. These are short extending posteriorly less than 
a: OS RE u nn U 
