98 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
longitudinally with regard to the ductus itself. The tube 
then turns round ventrally again, and runs as the axial 
structure of the cirrus. 
The latter, which is the aciual copulatory organ, is 
a cylindrical body tapering distally, and situated in the 
anterior half of the cirrus sac, lying nearly dorsoventrally. 
Its lumen is very narrow. Its internal and external walls 
are composed of the same ‘“‘ chitinous’’ substance as 
makes up the rest of the wall of the ejaculatory bulb. 
The penis is relatively thick, and the greater part of its 
wall between the limiting membranes is made up by a 
very dense connective tissue substance, consisting 
apparently of fibres running parallel to the ductus. The 
latter may project beyond the extreme tip of the penis. 
The greater part of the latter is contained within a 
sheath which is a reflection inwards, through the genital 
aperture, of the cuticular wall of the body. The sheath 
is continuous with the outer limiting membrane of the 
cirrus itself. Obviously the sheath is inverted when the 
cirrus is extruded through the common genital aperture 
in copulation. Two series of muscle fibres are connected 
with the cirrus and its sheath. One series (see fig. 3) 
originates in the inner wall of the cirrus sac, and 1s 
inserted round the cirrus at its marginal parts next to the 
sheath. The other series (possibly both may be the same) 
is inserted into the central part of the penis. 
The Female Genital Organs. 
The Ovary is situated very near the central part of the 
body, immediately anterior to the testis, and with iis 
posterior surface in close contact with the anterior surface 
of the latter organ. It is an oval body elongated in the 
transverse direction. At its anterior side, and a little to 
the left there is a prominent protuberance from which the 
