266 
A moehotaenia sphenoirles 
elliptical in longitudinal section with the greatest diameter at approxi¬ 
mately the anterior third of its length. At its apex, the anterior end 
has a narrow circular opening (o), leading by a channel of the same 
width into a dome-shaped chamber {d.c.) through the floor of which 
protrudes the muscular axis {a). The sheath (c.r.) consists of a dark 
staining structureless membrane, continuous with the body cuticle, 
inside which is a parenchyma similar to, but more compact than, the 
parenchyma of the body. 
The muscular axis is a narrow cylindrical organ, having anteriorly 
a terminal portion much wider than the remainder of the axis, from 
which it is separated by a deep constriction. This terminal portion is 
armed with a circle of hooks of the form characteristic of this genus, 
arranged with the heads nearly meeting anteriorly at its apex, and the 
hooks directed posteriorly, parallel to and in the same plane as the 
longitudinal axis of the rostellum. Posterior to the head, the remainder 
of the axis, after a shght bulge, tapers to a rounded extremity, the 
extreme end in the contracted condition being bent round upon itself 
so as to be directed anteriorly. The axis itself is formed of elongated 
muscles vdth distinct nuclei : its outer margin is formed by a dark 
staining membrane hke that of the sheath, surrounding a layer of 
circular muscles (c.m.) : the enlarged terminal portion in adchtion has 
an external layer of extremely thick and dense cuticle (c./n) in appear¬ 
ance much like the substance of the hooks. Thick muscles (r.ui.) extend 
from the sheath into the surrounding parenchyma and serve for the 
partial retraction of the sheath, the anterior end of which usually pro¬ 
trudes a little beyond the scolex (PI. XX, fig. 7). 
In the contracted condition, the enlarged terminal portion of the 
axis occupies and just fills the dome-shaped chamber in the sheath 
(PI. XX, fig. 5): when protruded, it projects from the anterior opening of 
the sheath, the lips forming the walls of the sheath being forced apart 
to allow of the passage of the body of the axis. In the extruded con¬ 
dition it can be seen that the walls of the dome-shaped chamber have 
only been pushed aside, not protruded: it follow^s, therefore, that the 
axis has simply elongated itself through the floor of the chamber and 
consequently is unattached to it, merely filling the opening. There are 
apparently no muscles connected with the sheath, except those for its 
retraction, so that the muscles necessary for the protrusion of the axis 
must be contained wdthin itself. The contraction of the circular muscles 
at the same time as the elongation of the longitudinal ones would cause 
an elongation of the axis as a whole, the extent of the elongation being 
