becomes intercellular.
Rarely the nephridium does not communicate with the coelom; in such
cases the nephridium ends in a single cell, like the "flame cell" of a
Platyhelminth worm, in which there is a lumen blocked at the coelomic
end by a tuft of fine cilia projecting into the lumen. This is so with
_Aeolosoma_ (Vezhdovsky). The condition is interesting as a
persistence of the conditions obtaining in the provisional nephridia
of e.g. _Rhynchelmis_, which afterwards become by an enlargement and
opening up of the funnel the permanent nephridia of the adult worm. In
some Polychaets (e.g. _Glycera_, see fig. 2) there are many of these
flame cells to a single nephridium which are specialized in form, and
have been termed "solenocytes" (Goodrich). They are repeated in
_Polygordius_, and are exactly to be compared with similarly-placed
cells in the nephridia of _Amphioxus_.

More usually, and indeed in nearly every other case among the
Oligochaeta and Hirudinea, the coelomic aperture of the nephridium
consists of several cells, ciliated like the nephridium itself for a
greater or less extent, forming a funnel. The funnel varies greatly in
size and number of its component cells. There are so many differences
of detail that no line can be drawn between the one-celled funnel of
_Aeolosoma_ and the extraordinarily large and folded funnel of the
posterior nephridia in the Oligochaete _Thamnodrilus_. In the
last-mentioned worm the funnels of the anterior nephridia are small
and but few celled; it is only the nephridia in and behind the 17th
segment of the body which are particularly large and with a sinuous
margin, which recall the funnels of the gonad ducts (i.e.
coelomoducts).

Among the Polychaeta the nephridium of _Nereis_ (see fig. 2) is like
that of the Oligochaeta and Hirudinea in that the coiled glandular
tube has an intracellular duct which is ciliated in the same way in
parts. The Polychaeta, however, present us with another form of
nephridium seen, for example, in _Arenicola_, where a large funnel
leads into a short and wide excretory tube whose lumen is
intercellular. In the young stages of this worm which have been
investigated by W.B. Benham, the tube, though smaller, and with a but
little pronounced funnel, has still an intercellular duct. That these
organs in Polychaeta serve for the removal of the generative products
to the exterior is pro