24 ON THE ANATOMY OF MEGASCOLIDES AUSTRALIS, 
distance parellel to the length or circumference of the body, and giving off or joining 
another similar duct from some other nephridium (neph.) The nature of the duct 
opening to the exterior varies in the clitellar and non-clitellar regions, and will be 
dealt with after the structure of the larger nephridia has been described. 
2.—Larger nephridia.—Their structure agrees in the main with that of the 
small ones, so far as the body of the nephridium is concerned. In both cases the 
ducts are so complicated, that as remarked by Bzepparp in connection with Acantho- 
drilus multiporus, it 1s simply impossible to map out the course of the duct. 
The differences between the large and small nephridia are, (1) the greater size of 
the larger, (2) the consequent greater number of the ducts cut in section. Of these 
some are thicker walled than others, and correspond exactly to those present in the 
smaller ones. The thinner walled ones, which are otherwise similar, are probably 
equivalent to the secondary ducts of other forms (such as Microcheta, &c.) and are 
absent in the part nearest to the attachment to the body wall. 
The supply of minute blood-vessels forming a complete network around the ducts 
is even more strongly marked than in the smaller ones. The blood-vessels to the 
large nephridia arise from a pair of vessels given off one on either side of the body 
from the ventral blood-vessel. The lateral vessels thus given off divide into two parts, 
of which one (Fig. 8, sept. bv.) runs to the septum, the other to the body wall 
ventrally and the nephridia. 
In Fig. 26 (Plate 6) is drawn a longitudinal section through the internal opening 
(Fig. 21, neph. v0.) of a large nephridium. The duct leads through the septum and 
swells out on the anterior face of this into the funnel-shaped opening. It is encased 
in connective tissue, amongst which are a certain number of muscle fibres (m.), 
circularly and obliquely arranged. External to the connective tissue and muscles is 
the layer of pavement ccelomic epithelium (c. ep.) The duct, almost up to the opening, 
is merely a continuation of the intra-cellular duct of the nephridium, and is ciliated. 
It is exceedingly difficult to determine exactly where the intra-cellular duct ends, and 
the inter-cellular begins. The cells lming the whole of the funnel have the curious 
homogeneous appearance characteristic of the nephridium, and the granules present in 
the cells in the body of the latter are here not so distinctly marked or radially 
arranged. It appears in many sections as if the duct right to the opening were 
intra-cellular, but after examining with high powers several series of sections, both 
transverse and longitudinal, I think that the drawing represents the real state of the 
case, and that the funnel has at its open extremity some three rows of cells serving to 
form the mouth of the funnel, and the internal opening of the nephridial duct into 
the body cavity. The cilia at the mouth are long, and at the entrance turned with 
their free ends towards the body cavity. 
External Openings of the Nephridia.—Brpparp has recently published a 
description of the relationships of the various nephridia and their external openings in 
Pericheta and Acanthodrilus, which has a most curious resemblance in many points 
