BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS- 335 



the usual granular contents, but the exterior firm setting-, so characteristically 

 wedge-shaped in other species, does not proceed half-way forwards, the slender 

 anterior portion having only a thin covering for its support, as indicated in the 

 figure. While in ordinary views the stylet and sac seem straight, both have a 

 decided curve when seen laterally (Plate VI. fig. 12). Just in front of the point 

 where the clear setting of the sac becomes indistinct, the ejaculatory duct opens into 

 the peculiarly elongated muscular cavity (e), which extends forwards to the cir- 

 cular opening in the floor of the anterior chamber. This channel shows a distinct 

 inner layer of longitudinal fibres, which, however, seem to act only in company 

 with the external oblique fibres surrounding them. The presence of this special 

 inner coat demonstrates that it is not the mere doubling of the floor of the 

 anterior chamber that forms this cavity, as indeed certain appearances, previously 

 observed, had led me to suspect. The central and lateral stylets have the same 

 shape, and the majority agree in size. In its usual position the stylet has the 

 form of a spear-head (Plate VI. fig. 13), being sharp -pointed, then dilating gra- 

 dually till near the posterior end, where a slight diminution occurs, and then a 

 marked constriction, just in front of the somewhat small head. If minutely 

 examined, both central and lateral stylets^ show a small secondary swelling or 

 ring above the head (Plate VII. fig. 9). The ejaculatory duct is comparatively 

 large and boldly marked, comprising at its posterior end almost the entire region 

 of the reservoir, a slight demarcation, however, marking off the dilated pos- 

 terior end into a portion pertaining to the reservoir, and another to the duct. 

 The widened posterior end is covered with small glands, which are continued 

 along the tube to its opening into the long muscular chamber behind the floor. 

 One peculiarity in the elongated reservoir is the comparative thinness of the 

 looped fibres towards the anterior end, and the thickness of the longitudinal 

 layer, which seems to afford compensation for the diminished strength of the 

 exterior coat. This deviation from the usual structure is doubtless in connection 

 with the enlarged posterior end of the ejaculatory duct, and the gradual con- 

 tinuation of the cavity of the reservoir into it. The bulk of the looped fibres is 

 grouped posteriorly, and in action would seem to compress the reservoir, so as to 

 throw its contents forward to the gaping aperture of the duct. On this account 

 also the posterior channel of communication is long. The external layer, con- 

 tinued from the preceding division, passes about half-way backwards over the 

 reservoir. Another peculiarity is the presence of numerous clear cells and 

 granules amongst the looped fibres, most distinctly seen at the posterior part of 

 the chamber. Some of the cells contain nuclei, and others do not. The glandu- 

 lar papillae in the interior of the reservoir are large and prominent. The very 

 great length of the posterior chamber as compared with the anterior is re- 

 markable. 



M. de Quatrefages seems to have devoted considerable attention to the ana- 



