A very remarkable genus, _Brachydrilus_, has lately been described by Dr. Benham,[413] in which each segment has two pairs of nephridia instead of a single pair. More recently, certain Australian forms, which I propose to unite on this account into a genus _Trinephrus_, have been discovered which have no less than three distinct and separate pairs in each segment.[414] [Illustration: FIG. 191.—Section through body-wall of _Megascolides australis_, highly magnified. (After Spencer.) 1, 4, 5, 6, Coils of nephridia; 2, funnel; 3, septum; 7, external apertures.] In many Megascolicidae there is a nephridial system of a different character. In _Perichaeta_ when dissected the nephridia appear, on account of their minute size, to be altogether absent. There is, however, in most Perichaetidae, in many Acanthodrilidae, and in many Cryptodrilidae a mass of minute tubules which cover the inside of the body-wall, and open on to the exterior by innumerable openings; there may be in a single segment one hundred or more of these external orifices, which are scattered about irregularly. It is at present uncertain whether these minute tubes are connected among {358}themselves, thus forming a network passing through the septum and from segment to segment, or whether each tube is isolated from its fellows, and forms a distinct nephridium, of which there are many in each segment and entirely separate. This is, however, certain, that the complex nephridial systems of at any rate _Octochaetus_ and _Megascolides_ are derived from the multiplication of a single pair of tubes which are alone present in the embryo. In _Perichaeta_ the minute nephridia are furnished with coelomic funnels; in _Octochaetus_ they are not, except in the case of certain nephridia which open into the terminal section of the intestine. Both at the anterior and at the posterior end the nephridia occasionally open into the alimentary canal. In various genera the first pair of nephridia are larger than the others, and open into the buccal cavity; it seems likely that they serve as salivary glands. A somewhat similar condition of things exists in _Peripatus_ (vol. v, p. 17). In _Octochaetus multiporus_, for example, there is a large tuft of nephridial tubes in the anterior region of the body, which opens by a long muscular duct into the buccal cavity. In the same species a good many of the nephridial tubes open into the posterior section of the intestine, reminding one of the anal vesicles of the Gephyrea (p. 436) and of the Malpighian tubes of the Arthropods. In many Eudrilidae the ducts of the paired nephridia form a network in the body-wall, which opens on to the exterior by many pores.