THE GIANT EARTH-WORM OF GIPPSLAND. 27 
There are one or two nuclei (n.*) close to the internal pole, the cells connected 
with which cannot be detected. They are similar in size and appearance to the 
nuclei of the cells forming the sphere, which again seem to be somewhat larger than 
those of the ordinary epidermic cells. 
Just where the duct enters the epidermic sphere are some 4-6 muscle cells, often 
with branched ends, which, from their arrangement, may be regarded as forming a 
sphincter for the opening of the duct, to the long axis of which they are placed at 
right angles (m.) Bxpparp, in describing a species of Acanthodrilus* in 1885, 
states that at the opening of the nephridium the columnar cells bend over towards 
each other on either side of the aperture. This appearance may perhaps be due to 
the development of a structure, such as is above described, but in his recent 
description of A. multiporus, he figures a different arrangement, in which the small 
cubical cells of the duct simply swell out into a sub-spherical shape within the 
epidermis. In the clitellar region, the ducts appear to pass right through the 
muscle layers, without branching as they approach the exterior. 
2.—In the posterior region of the body (Figs. 18 and 27) the ducts are somewhat 
different, and resemble much those of Acanthodrilus. A single duct has the 
appearance represented in Fig. 18. The intra-cellular portion resembles exactly that 
above described in structure, but when this has passed through the longitudinal 
muscle fibre layer, it opens just within the circular fibre layer into an extra-cellular 
duct, which may (Fig. 18) run straight to the exterior without branching, or may 
give off one or more branches. Its cells are cubical, and this part forms a strong 
contrast in structure to the same division in the clitellar region. The external 
opening shows precisely the same modification of the epidermic cells into a sphere, 
through the axis of which runs the duct. The muscle cells do not appear to be 
developed. The blood-vessel accompanying the duct is always present, though not 
in the form of a coil, and runs forward to form branches, which will ultimately ramify 
amongst the muscle fibres and the epidermic cells. 
Very frequently, in fact most generally, the duct leading to the exterior may, as 
soon as it has passed through the layer of longitudinal fibres, branch. This branching 
commences when the duct becomes inter-cellular (Fig. 27), and each duct of which, 
there may be two or three, has its own separate opening. 
There is no distinction between the ducts of the larger and smaller nephridia, 
and ducts passing to the exterior arise from the longitudinal duct which are not 
definitely in connection with special nephridia, and the branches of the various 
ducts may pass over in the body wall from one segment to another. 
In no part of the body is there any relationship between the nephridiopores 
and the sete, even when the nephridia become more localised. 
Such a relationship is described by Brpparp as occurring in P. aspergillwm, in 
the posterior region of the body. 
* Proc. RS. June 1885, p. 460. 
