246 Transactions of the Boyal Society of South Africa. 
through the middle of the cavity of this structure to communicate with the 
exterior at the extremity of the penis. 
At the base of penis there is a sUgbtly better development of tissue 
between the central canal and the outer epithelium, on the inner side of 
the latter. 
There can be little doubt that this penis is the correspondent of the 
solid penis as represented in other forms such as Gondwanaedrilus and 
Astacopsidrilus. Even in these forms the intermediate tissue is of a 
spongy indistinct nature. 
The special interest in this penial structure lies in the suggestion that 
we can now form possibly an idea of the significance of the atrial sac in 
such forms as P. heddardi and P. suhterraneus. 
In both these forms the atrium is enclosed in an " atrial sac " which 
extends practically from the point of entrance of the sperm duct into the 
attenuated portion of the spermiducal gland, to the extremity of the penis. 
The wall of this atrial sac is continuous with that of the penial sac. Now 
a transverse section through the penis of such a form as P. beddardi would 
be essentially similar to a section through the hollow penis of the newly 
described form. Further, a transverse section through the atrial sac and 
its contained atrium would also be essentially similar to a section through 
the penis of the new form, since the wall of the atrial sac is continuous with 
that of the penial sac. The strands of muscles which stretch across the 
atrial sac w^ould then represent the missing or degenerate intermediate 
tissue in the new form. If we imagine that the upper rim of the penial 
sac where it passes into the penis in P. heddardi were extended upwards 
to the point w^here the spermduct enters the spermiducal gland to form 
the atrium, and further that the w^all of the penis in the same form (which 
would now be greatly elongated) became or remained confluent with the 
wall of the atrial sac, we would then have the same structure in the penial 
sac and its contents as obtain in the new form. This is made clearer in 
the diagrams represented in the figures. 
In fact the penis of the new form is constricted as represented in the 
diagrams, and this constriction might w^ell correspond to the region of 
confluence of the penial wall and that of the atrial sac in P. beddardi. 
Female Organs. — The female pores, situated in the anterior region of 
segment xiii, have connected with them a short tube which passes 
upwards and forwards a short distance, and, piercing the septum, enters 
the xiith segment. The ovaries are attached to the anterior wall of seg- 
ment xii. Masses of developing ova are found in segments xiii, xiv, and xv. 
The masses in xiv and xv are contained in a sac in close apposition with 
(if not continuous with) the large sperm sac of those segments. Similarly 
the other masses are contained in thin-walled sacs. 
