ly very
large nephridia are not uncommon, and have been termed
"peptonephridia."

_Gonads and Gonad Ducts_.--The Oligochaeta agree with the leeches and
differ from most Polychaeta in that they are hermaphrodite. There is
no exception to this generalization. The gonads are, moreover, limited
and fixed in numbers, and are practically invariably attached to the
intersegmental septa, usually to the front septum of a segment, more
rarely to the posterior septum. The prevalent number of testes is one
pair in the aquatic genera and two pairs in earthworms. But there are
exceptions; thus a species of _Lamprodrilus_ has four pairs of testes.
The ovaries are more usually one pair, but two are sometimes present.
The segments occupied by the gonads are fixed, and are for earthworms
invariably X, XI, or one of them for the testes, and XIII for the
ovaries The position varies in the aquatic Oligochaeta. The
Oligochaeta contrast with the Polychaeta in the general presence of
outgrowths of the septa in the genital segments, which are either
close to, or actually involve, the gonads, and into which may also
open the funnels of the gonad ducts. These sacs contain the developing
sperm cells or eggs, and are with very few exceptions universal in
the group. The testes are more commonly thus involved than are the
ovaries. It is indeed only among the _Eudrilidae_ that the enclosure
of the ovaries in septal sacs is at all general. Recently the same
thing has been recorded in a few species of _Pheretima_ (=
_Perichaeta_), but details are as yet wanting. We can thus speak in
these worms of _gonocoels_, i.e. coelomic cavities connected only with
the generative system. These cavities communicate with the exterior
through the gonad ducts, which have nothing to do with them, but whose
coelomic funnels are taken up by them in the course of their growth.
There are, however, in the _Eudrilidae_, as already mentioned, sacs
envolving the ovaries which bore their own way to the exterior, and
thus may be termed coelomoducts. These sacs are dealt with later under
the description of the spermathecae, which function they appear to
perform. The gonad ducts are male and female, and open opposite to or,
rarely, alongside of the gonads, whose products they convey to the
exterior. The oviducts are always short trumpet-shaped tubes and are
sometimes reduced (_Enchytraeidae_) to merely the exter