144 DR. W. B. BENHAM ON [Feb. 16, 



at the tip ; and projecting from this pit is a smaller whitish papilla 

 provided at its apex with a minute pore (Plate VII. fig. 7). 



I expected, at first sight, that the hinder pair of the papillae 

 would be in connection with the sperm-ducts, but no such relation 

 exists. Each of the four papillae is represented internally by a 

 rounded or kidney-shaped swelling (Plate VIII. fig. 9), from the 

 centre of which (or from the hilum as the case may be) there passes 

 to the body-wall a bundle of fibres (m). These are muscle-fibres 

 and surround a " chsetophore " or sac containing the chsetae, which, 

 replace the ordinary ventral chaetse, from whicli they differ only in 

 their greater length. 



The papilla itself has the following structure (which is closely 

 similar to that of the next species, of which a figure is appended 

 (Plate VIII. figs. 10, II) : the pore at the apex of the inner papilla 

 (pap.) leads into a sac lined by columnar cells {ep.) forming a definite 

 epithelium ; the lumen of the sac extends in an irregular way for 

 some distance all round the aperture, and its epithelium is, at places, 

 considerably folded. Outside the epithelium are numerous bundles 

 of muscle-fibres (mus.), some radially arranged, some circularly, and 

 some longitudinally (as seen in a transverse section of the body-wall 

 passing through the papilla). These fibres can be traced into the 

 muscular layers of the body-wall, from which they are evidently 

 derived by its invagination. Outside the muscular coat — though 

 not separated from it by any marked line such as the figure 

 suggests — is a thick coat of clitellar cells arranged in groups (fig. 

 llfffl.). Blood-vessels ramify between the groups and amongst the 

 muscle-bundles. Surrounding the whole is a layer of flattened 

 cceloraic epithelial cells (co.ep.), which dips down between the 

 groups of clitellar cells. The muscle-fibres are found only near the 

 aperture in that part of the organ which forms the external papilla ; 

 in the remainder of the gland the clitellar cells abut immediately 

 upon the epithelial cells. 



There is a remarkable resemblance in structure between this organ 

 — which is evidently copulatory in function and capable of slight 

 eversion — and the prostates (or atria) of Perichceta, Acanthodrilus, 

 Trigaster, &c. ; the epithelium, however, is more definitely marked 

 off from the gland-cells than in these, and recalls, rather, the pros- 

 tates of Pontodrilus ; or if we compare the structure of the organ 

 near its pore with the atrium of Moniligaster we shall see a still 

 greater resemblance, except that in the latter genus there is, ac- 

 cording to Beddard's description ^, no membranous coelomic epi- 

 thelium, for the " clitellar cells " represent this layer. 



Amongst the families Bhinodrilidce, Geoscolecidce, and Lumbri- 

 cidcE, a " prostate " is not usually recognized as being present, but 

 in several genera there is a more or less conspicuous swelling of 

 the body-wall, which is perforated by the sperm-duct in its passage 

 to the exterior. In Geoscolex, Brachydrilus, Griodrilus, and Oalli- 

 drilus such structures exist ; of the histology of these, however, 



1 Q. J. M. Sc. xxix. pp. 119 &c. pi. xii. fig. 11. 



