Cameron. — i\'c/i/i>i'f/hirii of Maoridiiliis rosae Bedchnd. 187 



taining small uuclei {r.t.ii). This' nucleated layer repreaenta the connective 

 tissue of the bladdev-wall : it is not vesicular in Maoridrilns. In it the 

 muscle-fibres are embedded : these fil:»ies form a network over the wall of 

 the bladder ; they are long- and fine, and cross it in all directions — longi- 

 tudinally, transversely, and obliquely. Towards the pore the fibres con- 

 verge, and are seen in section to become continuous with the muscles of the 

 circular layer {cm) of the body-wall. 



On the inner side of the muscular coat are seen large niicleolated nuclei 

 (fig. 11, hh) embedded in a layer of protoplasm slightly more granular 

 and more darkly staining than the connective-tissue layer. The nuclei are 

 often coitained in the processes {fr) of the inner wall of the bladder which 

 ])roject into the lumen ; these are very noticeable in a transverse section 

 of the bladder, the lumen of which has a most irregular outline. 



The structure of the wall at this point presents the same difficulty of 

 interpretation as was experienced in Luinhricus, for in Maoridrilus also it 

 is difficult to detect the outlines of the cells. Although in section one 

 nucleus, oi- at most two or three, are seen, the lumen is of an intercellular 

 nature, the cells forming the epithelium l:)eing large and comparatively f e^ . 

 As may be seen in a glycerine preparation, where they shine through the mus- 

 cular fibres and coelomic eiiithelium (fig. 6), they are clearly too numerous 

 to belong to a series of perforated cells. In fig. 11, taken from a series of 

 longitudinal horizontal sections, the external pore of the nephridium is 

 seen to be formed by an invagination of the epidermal cells. The short 

 duct formed thereby is without the slightest doubt intercellular ; and this 

 duct joins the short tubular region {n.t) of the distal end of the bladder, 

 where the cells are becoming very similar to the epiblastic cells, and are 

 clearly forming an epithelium round an intercellular lumen. As this part 

 widens out to form the dilated bladder the nuclei become larger and farther 

 apart, till the}' l^ecome relatively scarce and the cells of the epitlielium 

 relatively enormous : but the cell-boundaries cannot be detected in the 

 dilated region. 



The histological structure of the various parts of the canal agrees with 

 the descriptions given by previous authors for the nephridia of other genera, 

 so that it is unnecessary to describe it once again. 



In many specimens I noted excretory vesicles in the lumen of the 

 inner narrow tube, and globules of fluid were seen in the protoplasmic wall 

 of the canal. But excretory globules are chiefly confined to the wide duct 

 ((•/. Benham, 10). 



The bridge canal does not differ greatly in its structure from the narrow 

 tube, excejjt that it is ciliated in two rows, and that it contains a number 

 of vacuoles lying against the boundary of the lumen. These are probably 

 excretory globules which dischaige their fluid into the lumen of the duct. 



The structure of the nephrostomial duct (fig. 4) is rather noteworthy. 

 It is not, as is generally the case, formed of perforated cells, but is 

 relatively wide, and is surrounded by a distinct epithelium of fairly large 

 cells. The nuclei are not ]ilaced as closely together as is general in an epi- 

 thelium, and from four to six only appear in a transverse Section. Such a 

 structure for the ne])hrostomial duct does not seem to have ])een recorded 

 in other eai'thwoiins. 



Vascular ^^apply oj the Nej)hridiui)i. 

 The general course of the vessels connected with the nephridium agrees 

 with that in Lmnhricus as given by Benham, and with that in Moniligaster 

 as described by Bourne, so that it is needless to go into details. 



