27 
about one-ninth to one-seventh of the length of the worni from the 
oral margin. 
Acetabulum . — Measurements of the acetabulum taken from press 
preparations make it about 2.6 mm. in longitudinal diameter by 2.75 
to 3 mm. in transverse diameter. The aperture is rather oval in out- 
line, about 1.55 mm. in transverse by 1 mm. in longitudinal diameter. 
INTERNAL ANATOMY. 
Digestive tract. — The anterior bluntly pointed, attenuated ex- 
tremity (cephalic cone) is pierced by the mouth, which is not provided 
with a true sucker. The oral margin is surrounded by a number 
of slender, digitate papillae. The mouth gives entrance to a muscular 
pharynx; the lumen of the latter is at first more or less circular in 
transverse section, but it rapidly becomes flattened and crescentic 
with the convexity of the crescent dorsad. From the horns of this 
crescent spring two lateral pouches and the lumen of the pharynx 
terminates blindly as a narrow crescentic slit connecting the two lat- 
eral pouches. From the ventral aspect and a little above the blind, 
slitlike termination of the lumen of the pharynx, the esophagus rises 
and passes caudad, forming a ventral curve in its course. At its 
point of origin it communicates laterally with the lumen of the 
pharyngeal pouches, between and a little ventrad of which it lies. 
The relation of the esophagus to the pharyngeal pouches and blind 
slit will be seen by reference to figures 32 to 36. 
At about one-fifth of the total body length from the oral margin 
of the worm, the esophagus divides into two simple cecal tubes which 
pass at first laterocaudad, then in slight A tortuous line caudad to 
about the level of the cephalic margin of the acetabulum. Just before 
reaching their termination they shift a little toward the median 
line. One tube may be somewhat longer, and so terminate at a 
slightly lower level (more distal) than the other. In their course 
they are wavy and are separated by a distance about equal to that 
which separates them from the corresponding lateral margins of 
the worm. The pharynx, pharyngeal pouches, and esophagus are 
lined by a cuticle in anatomical continuation with that of the surface. 
At the esophageal fork this lining abruptly ceases, the intestinal 
tubes being lined by a nucleated epithelium. 
Genital system. — Male organs: The two testicles lie in the ceph- 
alic half of the area included between the intestinal ceca, and are 
somewhat nearer the dorsal than the ventral surface. (Fig. 31.) 
One is directly caudad of the other, the two being separated by a 
narrow interval which is partially occupied by some coils of the 
uterus. The anterior testicle is somewhat smaller than the posterior 
and in press preparations their outlines are sinuous, but sections 
