STUDIES ON THE DIGENELIC TREMATODES. 4.07 
(15-2 mm.) and the intestinal bifurcation occurs a short 
distance in front of the ventral sucker. The diverticula are 
uniform and fairly wide, extending almost to the posterior 
end of the body. The cesophagus is lined by a somewhat 
thick membrane (metamorphosed epithelium), the surface of 
which is thrown into slight folds. This membrane is con- 
tinuous with the cuticular lining of the pharynx, but is thicker 
and stains differently. With hemalum-eosin it takes on a 
reddish-purple colour, whereas the cuticle is more distinctly 
blue, The musculature consists of the usual internal annular 
and external longitudinal layer, the fibres being more or less 
widely separated according to the degree of contraction. 
Surrounding the outer layer is a ring of very loose connective 
tissue, on the outer edge of which are numerous small, blue- 
staining cells—the myoblasts of the cesophageal muscles. 
The diverticula separate at a wide angle and bend towards 
the outer side of the ventral sucker. The rest of their course 
is practically straight, with a slight turn in near the end. 
At first they lie midway between the dorsal and ventral 
surfaces of the body, but on passing the ventral sucker they 
assume an unvarying dorsal position and are surrounded on 
all sides except dorsaliy by the yolk-glands. The average 
width of each diverticulum isabout ‘08mm. Their transverse 
section appears sometimes oval, sometimes triangular, and 
sometimes almost circular. The lining consists of a single 
layer of epithelial cells, with well-marked nuclei and nucleoli. 
The nuclei measure ‘005-008 mm. The cells are of irregular 
shape, with long fibrillar or hair-like processes stretching into 
the lumen and filling it up to some extent. Amidst the cells 
there are numerous small vacuoles. The appearance presented, 
in fact, is that of a row of nuclei lying in the midst of a fibrous 
feltwork ; the cell outlines are difficult to distinguish. This 
epithelial layer is absent in a small part of the diverticula 
just behind the bifurcation, and is replaced by a continuation 
of the cesophageal membrane. This recalls the condition in 
Patagium brachydelphium Heymann, in which thie 
initial part of the diverticula is constricted and devoid of 
VOL. 53, PART 3.—NEW SERIES. 29 
