4g ON THE ANATOMY OF MEGASCOLIDES AUSTRALIS, 
until it completely merges into the rest, and nothing but small nephridia are present, 
which, as the anterior end of the body is approached, cover the whole body wall 
internally. In addition to this, where the larger nephridia are present, there exist 
(1) a network of ducts connecting the smaller nephridia in each segment, and (2) a 
well-developed longitudinal ventral duct on each side, running from the smaller 
nephridia forwards to the larger nephridium, and then continued on, but much finer 
in structure, to the ventral surface of the next segment, where it communicates with 
the longitudinal duct passing to the next large nephridium. 
These series of structures reveal (1) the method of formation of the large 
nephridium from an aggregation of small ones, with a subsequent formation of an 
internal opening, and (2) the loss of a continuous network in the anterior part of the 
segment, as the smaller nephridia have become aggregated towards the ventral 
surface, still retaining their connection with the other nephridia, and hence the final 
result of a ventral single duct when the single nephridium becomes established. 
In Megascolides, all the smaller nephridia are not, so to speak, used up in 
forming the one pair of large nephridia, but we can easily suppose a case in which, as 
in Pericheta aspergillum, there is primitively a large number of nephridial tufts in 
each segment, with a network continuous from segment to segment. If these 
become aggregated, so as to form a single pair of nephridia in each segment, then as 
they pass down towards the ventral surface (supposing the aggregation, as has 
usually happened, to take place in that direction), the network still connecting the 
nephridia, if it persists at all, will eventually assume the form of a longitudinal duct, 
passing from one group of nephridial tufts or one single nephridium, according to the 
stage of development arrived at, to the next in order along the ventral surface. 
It will be seen from this that there is no necessity to assume that a longitudinal 
duct, when present, is the homologue of a longitudinal duct of a Platyhelmunth, but is 
rather to be regarded as a modification of the network of ducts brought about 
by aggregation of the nephridia (1) into a series of tufts, and (2) the further develop- 
ment of these into large nephridia. The simplest nephridial systems of Hirudinea 
and Chetopoda alike, present no structures similar to the longitudinal duct of a 
Platyhelminth. This, at all events, does away with the necessity of supposing a 
double origin for the nephridial systems of Chetopoda,* one from ancestors with a 
network of ducts, the other from ancestors with a pair of longitudinal ducts, and at 
the same time, upon different grounds, brings us to the same conclusion as BEpDARD— 
“that the longitudinal ducts of Lumbricus, Lanice, &e. (we may now add 
Megascolides), have not any relationship to that of the Platyhelminths.” 
One great difficulty remains in the fact that, according to Wutson, the 
longitudinal duct in the embryo Lumbricus is epiblastic in origin. Until the 
development of the nephridial systems in the various forms has been consistently 
* BEDDARD, Op. cit. P. 408. 
