88 THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 
Rhynchodemus, according to von Kennel (whose observations are supported by the 
earlier ones of Moseley on the same genus) the vas deferens springs from the last 
testis. In Geoplana traversi, again, Moseley states that a wide vas deferens leads 
from the hinder end of the testes transversely inwards to the vesicula seminalis. 
In Geoplana spenceri, on the other hand, the vas deferens commences near the 
anterior end of the body, probably at the level of the first pair of testes, and it lies 
just inside, instead of outside of the nerve cord of its side and just below the 
transverse commissures between the two cords, as shown in figure 4, v.d. From this 
position it follows that the testes cannot communicate directly with the main vas 
deferens, and as a matter of fact each testis communicates with the vas deferens of 
its side by means of a narrow and rather long branch which starts from the broad 
ventral aspect of the testis and runs transversely beneath the nerve cord to enter the 
vas deferens at right angles. This arrangement is best seen in horizontal sections, 
when the vas deferens with its branches appears as shown in figure 31. 
It seems to me not improbable that a condition similar to that which I have 
described may be found to exist in Rynchodemus and Geoplana traversit. 
On nearing the penis each vas deferens becomes dilated to form a thin-walled, 
tortuous vesicula seminalis; they then contract again and unite at the base of the 
penis to form the convoluted duct which leads through the penis to the genital 
orifice (Fig. 43, d.). The vasa deferentia and their branches are lined by a very thin, 
flattened epithelium of nucleated cells (Fig. 81), but in the vesicule seminales the 
cells forming this epithelium become more or less cubical. 
(c) The Penis.—This is an ovoid, muscular mass, tapering towards the posterior 
end, which is directed downwards towards the genital aperture. It lies immediately 
in front of the vagina, and can be readily dissected out, together with the’ female 
copulatory organ, as a definite structure, when it appears as shown in figure 32. Itis 
pierced throughout its length by the duct, convoluted at the anterior end, through 
which the spermatozoa are discharged (Fig. 48, d.). The muscle fibres of which the 
penis is composed are arranged in two principal sets, circular and longitudinal, the 
fibres of the two sets occurring intermingled with one another. The duct of the 
penis is lined by a layer of small, deeply staining, columnar, ciliated cells. 
The penis of Geoplana spenceri is remarkable for the fact that it does not le for 
the most part free in a surrounding cavity, as for example in Szfalium (6), 
but is closely surrounded by the general tissues of the body almost up to its 
termination near the genital aperture. The capability of protrusion of the penis 
under these circumstances must depend upon the great elasticity of the surrounding 
tissues. 
