I 
ANDREWS: ANNULUS VENTRALIS. ' 455 
The sperm placed by the male in the annulus, filled all the posterior 
part of the trumpet tube as shown in figure 21 (pi. 46). When the 
annulus was dried and broken open, the contents of the tube came 
out as a flat, curved plate of wax-like substance which in water swelled 
up and allowed sperm to spread out from its tip and from any broken 
part. The posterior part of this cast of the cavity of the annulus pre¬ 
sented a slight enlargement to fit the terminal enlargement of the 
tube shown in figure 21 (pi. 46). 
The position of the annulus is that found in C. affinis (text-figure 
A), and it is also hinged to the concave sternal plate anterior to it so 
that its posterior edge may be pushed dorsally to displace the soft 
tissues above it but cannot be pulled downward below the horizon¬ 
tal position it assumes when left to itself. The annulus differs from 
that of C. affinis (pi. 43, fig. 1) in being larger and truly annular in 
appearance as seen in figure 29 (pi. 47). The large central depressed 
area is surrounded bv a high rounded rim, or ring. The posterior 
half of the rim passes gradually into the depressed area, anteriorly. 
But the anterior half of the rim stands up away from the depressed 
area as two bolsters or cushions, one right, one left of a median groove. 
These cushions may be indented by a needle point and in life they are 
.sometimes red while the posterior parts of the annulus are greenish 
or bluish, but often the entire organ is creamy white. Only the pos¬ 
terior half of the annulus is well calcified and when cleared in oil of 
cloves this part remains opaque white while the anterior half looks 
like translucent ehitin. 
The zigzag suture coming from the posterior face over the rim 
passes, like a stream at the bottom of a valley, forward and downward 
across the depressed area to disappear under the anterior cushion on 
the right. In its course the zigzag presents six successive component 
lines. Thus, leaving the median plane, it passes a short distance to 
the right, then a longer distance to the left, then a shorter distance to 
the right, nearly parallel to its second course, then a long distance to 
the right and finally forward and somewhat to the left under the cush¬ 
ion. Of the five angles along its course, the second and third from 
the posterior end are marked by long extensions of the line beyond the 
point of meeting the next line of the zigzag. Most of the length of 
this line is a mere closed groove, but the anterior two stretches are wide 
open clefts becoming anteriorly an open orifice under the cushion. 
The floor of the depressed area juts out right and left in hills and 
