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FRANK E. BEDDARD. 
me to necessitate this view of the gradual reduction of the 
excretory system ; it is difficult to harmonise the facts with the 
hypothesis of one continuous line of development. 
It is obvious that any theory of the development of the 
nephridia must allow for the reduction of the nephridial net- 
work in Perichseta aspergillum to a single pair of ne- 
phridia, such as is found in P. novae-zealandiae, 1 and also in 
the genus Perionyx, which is in all respects a very near ally 
of Perichseta; and this reduction must not involve the 
various stages represented by Deinodrilus, Acantho- 
drilus, and Dichogaster, though these are intermediate 
between P. aspergillum and P. novae-zealandiae. 
The intermediate stage between P. aspergillum and P. 
no vae-zealandiae is represented by P. armata. In this Peri- 
chaeta the nephridia of the posterior segment are, as Spencer 
pointed out in the case of Megascolides, separable into two 
categories ; firstly, there are the tufts of minute tubules ; 
secondly, a pair of convoluted nephridial tubes, with a ciliated 
funnel borne upon the extremity of a tube which has traversed 
the septum, and lying in the segment anterior to that which 
contains the nephridium ; these latter are of the same calibre 
as the nephridia of P. novae-zealandiae, and indeed of most 
Earthworms in which there is but a single pair of nephridia 
per segment. I believe that these have originated from the 
somewhat larger nephridial tubules of such a form as P. 
aspergillum; the minute nephridia form tufts which are 
largely, if not entirely, isolated from each other and from the 
large nephridia; they are comparatively inconspicuous, and 
seem to be in course of disappearance. Megascolides offers 
an analogous stage in the development of a single pair of 
nephridia out of the nephridial network. I quite agree with 
Spencer that the single pair of nephridia of certain 
Earthworms (e. g. Perichaeta novae-zealandiae and 
Perionyx) have arisen by a gradual increase in 
1 This is an apparently new species of Perichseta, which I hope to 
describe shortly ; it possesses a single pair of nephridia per somite, as in 
Lumbricus. 
