STRUCTURE OF UROCH^TA AND DICHOGASTER. 275 
external pores. The network is not interrupted by the septa, 
and the external pores are not in any way related to the seg- 
mentation of the body. If funnels are really absent, as appears 
to be the case, then the termination of the tubules in single 
cells will be an additional point of resemblance to the Platy- 
helminths ; if, on the contrary, funnels are really present, 
they must be small and inconspicuous and not much advanced 
beyond the single flame-cell . 1 
In the posterior segments part of the nephridial network 
consists of tubules of a greater calibre, and these, as well as 
the smaller tubules (which are exactly similar to those of the 
anterior segments), are provided with funnels. The external 
apertures are still extremely numerous, and irregularly distri- 
buted over the surface of the body. The network of tubules 
is beginning to break up into more or less isolated tufts ; but 
the separation of the continuous network into isolated nephri- 
dia has no discernible relation to the segmentation ; the tufts 
of tubules have no regular arrangement within the segment, 
and the septa do not as yet form barriers between the excretory 
tubes of different segments. 
In the posterior segments, therefore, the primitive characters 
of the nephridial system are just beginning to disappear. If 
the posterior segments resembled the anterior segments the 
nephridial system of P. aspergillum would exhibit the pre- 
sumed ancestral condition. 
From this point the modification of the excretory system 
has, as I think, proceeded along two slightly divergent paths; 
the ultimate point reached, however— the reduction of the 
nephridial system to a pair of isolated nephridia in each seg- 
ment — is the same in both cases. The facts known appear to 
1 I have already (1) discussed the “ funnel ” of the Annelid nephridium 
and its relation to the Platyhclminth flame-cell. Since that paper was written 
Yejdovsky has published (‘ Zool. Anzeiger,’ Bd. x) an account of the nephridia 
of certain Oligochseta. The " provisional ” nephridia, which are preceded at 
the anterior extremity of the body by a “ larval ” set, terminate in a flame-cell. 
These nephridia entirely disappear in the first two or three segments; behind 
this they become converted into the permanent nephridia; the flame-cell 
divides and gives rise to a funnel. 
