ANDREWS: ANNULUS VENTRALIS. 
467 
The remarkably transverse position of the tube is appreciated when 
a decalcified cleared specimen is looked at from the ventral side (pi. 
46, fig. 26). Here the suture is indicated by the two dark lines. The 
short one passes from the middle of the posterior edge of the annulus 
to the right and soon meets the long second line sweeping forward 
and to the left. The other dark line on the left indicates the edge of 
the abrupt overhanging left rim of the central depression. This edge 
running as the left edge of the groove of the anterior face and 
coming into the depressed area, sweeps to the left, and then re¬ 
turns towards the median plane to cross the suture line. The short 
chink formed between these two lines is the right end of the trans¬ 
versely placed orifice of the annulus. The rest of the orifice is still 
farther to the left under the overhanging rim that conceals the left end 
of the tube. The tube, or cavity, of the annulus is shown as a narrow 
clear space passing from the above orifice far over to the right of the 
annulus and then posteriorly to end as a marked enlargement or bulb. 
This terminal bulb of the tube is on the right of the median line. 
Just posterior to this bulb is a small but marked recess. In some 
of the right-handed annuli the recess was posterior, and in others 
partly to the right and in others partly to the left. In the two left- 
handed annuli examined there was also no constant position of the 
recess with reference to the median plane. 
The connection of the recess with the bulb or end of the trumpet 
tube, was not seen in several surface views but in figure 25 (pi. 46) it 
was very evident. Here the recess on the right opens anteriorly into 
the large bulb and posteriorly a fold of exoskeleton intervenes as a 
wall between the two spaces both of which contain some sperm. This 
figure also indicates the way in which the tube of the trumpet connects 
with the closed suture on the surface of the annulus. The suture is 
shown as a series of heavy black lines from which planes were seen to 
pass toward the tube of the trumpet. The dorsal ends of these planes 
are indicated by the broken lines. As these planes are narrow chinks 
or clefts they would allow the sperm to pass to the suture. Anteriorly 
and to the left the plane is a transverse one sloping from the suture 
posteriorly. Anteriorly and to the right, the plane is a much bent 
one whose anterior and posterior halves are nearly at right angles with 
each another. This plane slopes to the right and anteriorly. Poste¬ 
riorly, a plane passes from the suture to the left but nearly at right 
angles to the plane of the paper. All these planes open dorsally into 
