46 ON THE ANATOMY OF MEGASCOLIDES AUSTRALIS, 
(2) Those with numerous small nephridia in each segment, similar to those in 
(1), and with, in addition, large nephridia in certain segments with internal openings 
(only example known as yet, Megascolides). 
(3) Those with a limited number of large nephridia only in each segment— 
usually one pair (Lumbricus, &c.) 
Now of these three divisions, there can be little doubt that the one characterised 
by the presence of a great number of nephridia scattered over the body wall without 
definite arrangement is in a more primitive condition, as far as its nephridia are 
concerned, than the one characterised by the presence of a single highly-developed 
pair in each segment of the body. Such a worm as P. aspergillum, with its very 
numerous scattered nephridia, stands in very much the same relationship to other 
worms in this respect as that in which Peripatus stands to other Arthropods in the 
matter of tracheal tubes. 
There is only one other course open, and that is to regard the condition found in 
LIumbricus as a primitive one, and that in Acanthodrilus as not more highly developed, 
which could scarcely be held but degenerate. This view might be held, but there is, ~ 
so far as I can see, no evidence in its favour, and it would be contrary to all analogy. 
We must regard P. aspergiulwm as more primitive in its nephridial system than 
Iumbricus. Between them and bridging over the great differences in structure in 
these two extreme types come (1) Acanthodrilus, and (2) Megascolides. In both of 
these we get differentiation, rendering them more highly developed than Pericheta, 
and giving indications of the final state reached in Lumbricus. 
The most primitive nephridium with which we are hence acquainted in 
Olugochete has no internal opening resembling in this respect the ancestral 
Platyhelminth, from which it may be supposed to have been derived. Such nephridia 
are characteristic of P. aspergillum and A. multiporus, which do not appear to have 
yet reached the stage in which the secondarily-formed ciliated funnels place the 
nephridial ducts in connection with the ccelom. 
In the Perichete worm, the small nephridia are in their most primitive condition, 
and still irregularly scattered; but in Acanthodrilus and Megascolides the system is 
somewhat more highly differentiated. In both of them the modifications commence 
at the posterior end of the body, resulting in the former in the aggregation of the 
nephridia corresponding with the setze in position, and in the latter in the formation 
posteriorly of large nephridia with internal openings. At the anterior end the small 
nephridia are present in such enormous numbers, more especially in the segments 
containing the genital organs, that they line closely the whole body wall. 
At the same time, the genital ducts and copulatory pouches are equally highly 
developed in all the forms. It thus follows that genital ducts, highly developed, 
and consisting, amongst others, of vasa deferentia, traversing no fewer than seven or 
eight segments, are developed in certain earth-worms (Pericheta and Acanthodrilus), in 
which the very numerous primitive nephridia have no internal openings; and in another 
