666 DAVID HILT TENNENT. 
which are provided with a lining resembling the cuticle 
covering the surface of the body. ‘This ceases abruptly at 
its contact with the intestinal epithelium. 
The wall of the gut consists of a single layer of vacuolated 
cells, which le on an extremely thin basement membrane. 
These cells are irregular in outline, and remind one of the 
endoderm cells in Hydra. A deepiy-staining nucleus may 
be seen toward the base of each cell, while the vacuoles 
occupy a position toward the opposite end. 
Ziegler (7), in describing the gut in G. fimbriatum, 
mentions an irregular row of nuclei and the vacuolated 
appearance of the intestinal epithelium, but was not able to 
observe cell boundaries. 
In my sections there is present in every instance a definite 
layer of lightly-staining material extending from the ends of 
the digestive cells into the cavity of the gut. This layer 
seems to consist of exceedingly fine fibres or threads (fig. 53, 
ppr:)- 
Looss (47, 1894) described a similar condition of the 
intestinal epithelium in several distoma. Juel (48, 1889), 
for Apoblema species, and Lander (49, 1904), for Hemiurus 
crenatus, describe a portion of the gut as being so modified. 
Sommer (50, 1880) describes and figures the inner ends of 
the gut cells of Distomum hepaticum as extending either 
in a network of coarse pseudopodia or in fine threads. 
The appearance in G. gracilescens is probably due 
to the same cause, i.e. is caused by the protrusion of the 
substance of the gut cells into exceedingly fine protoplasmic 
processes, which function in the absorption of food. 
In the wall of the gut are two sets of diagonal muscles, 
crossing each other at right angles. 
Tue Nervous System. 
The brain lies just behind the sucking disc. As in Buce- 
phalus, it consists of. a fibrous mass in which a few scattered 
ganglion cells are embedded (fig. 57). The cell bodies, 
