H. S. Pratt 
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the cirrus is not extended and the body is much contracted, the cirrus 
sac (6) and the metraterm (24) are seen to be of equal length and to 
extend more than two-thirds of the distance between the acetabulum 
and the ovary and to be thrown into a series of irregular coils. 
The outer wall of the cirrus sac (Figs. 6 and 7, 46) is a musculature, 
the fibres of which form a sort of felt and do not fall into circular and 
longitudinal layers although they have a general circular direction. 
Within this wall is the characteristic vesicular parenchyma in which 
are embedded numerous parenchyma cells (30). 
The hinder fifth of the cirrus sac has a somewhat greater diameter 
than the forward portion and contains the vesicula seminalis (Figs. 1 
and 2, 45). The remaining four-fifths forms a long slender tube which 
tapers slightly toward the forward end where it joins the genital sinus. 
Immediately anterior to the vesicula seminalis in this portion is the 
prostate region (35) which is short and contains the rather sparsely 
distributed prostate cells. The remainder of the lumen of the cirrus 
sac, constituting the anterior half or two-thirds, may be called the 
cirrus (Fig. 2, 5), of which only the anterior portion, however, can be 
extruded to form a functional penis (Fig. 1, 5). 
The structure of the cirrus is similar to that of the genital sinus. 
Its lumen is bounded by a cuticula (Fig. 6, 8) which, like that of the 
genital sinus, is thickly set with perpendicular bristles. These extend 
through the entire thickness of the cuticula and into the lumen of the 
cirrus, giving it a very characteristic roughened surface. 
It is only near its anterior end, however, that the cuticula has the 
character shown in Figure 6. A short distance back of the anterior 
end the perpendicular cuticular bristles become somewhat more delicate 
and embedded among them appear sparsely scattered spines of large 
size and peculiar construction. These spines are scattered at regular- 
intervals and are very conspicuous objects (Fig. 7, n). Each one 
consists of a bulbous base (Fig. 8, 3) which is embedded in the cuticula, 
lying near its outer surface, and a high cylindrical rim (13) which 
extends from the bulbous base to the inner surface of the cuticula. 
The total length of the bulbous base and the rim is thus equal to about 
the thickness of the cuticula of the cirrus. Extending now from the 
bulbous base through its cylindrical extension is a long slender spine 
which reaches beyond the general surface of the cuticula far into the 
lumen of the cirrus (Fig. 7, ll). 
The structure of these peculiar spines is even more complicated than 
this description indicates. The bulbous base, which is spherical in 
