PROBOSCIS. 67 



posterior chamber than in A. lactifloreus. The anatomy of the muscular and other tissues of the 

 proboscis in Tetrastemma agrees with that in Amphiporus. 



In Prosorhochmus Claparedii the stylet-region (Plate XIII, fig. 1) has the granules of the 

 external circlet of glands unusually large and distinct. The basal apparatus of the central 

 stylet has a straight border and sharp angles posteriorly, and obtuse angles at the sides. 

 The pale investment of this structure is comparatively limited in bulk ; and the curved fibres 

 immediately behind sweep outward and forward very distinctly. 



The size of the proboscis in Nemertes gracilis is greatly diminished in proportion to the bulk 

 and elongation of the animal, the stylet-region, indeed, being found only a short distance behind 

 the ganglia (Plate XII, fig. 11). The floor of the anterior chamber generally presents a bilobed 

 aspect under examination, and has not the massive muscular structure usually found in front of the 

 stylet-sacs ; but it is furnished with a somewhat opaque mobile lobulated arrangement of glands, 

 which, in extrusion of the organ (Plate I, fig. 6), appear as two semi-opaque whitish papillae (one 

 on each side), the stylet-sacs being prolapsed into their interior. The central stylet does not 

 easily project in this condition. The stylet-region proper is somewhat opaque, on account of the 

 glandular nature of the walls anteriorly, and the layer of granular glands posteriorly. The latter 

 are placed far back, and in developing specimens form a granular mass on each side of the 

 ejaculatory duct, sometimes entirely filling up the space (at a, Plate XII, fig. 11) ; and consist 

 of a dense aggregation of minute clear granules, and coarsely lobulated glands, which are appa- 

 rently homologous with the granular glands of other species. The marginal stylet-sacs have 

 very long ducts, and each encloses from seven to ten stylets of a distinctive shape, besides 

 other contents. The central stylet is appended to a basal apparatus of great length, its outline 

 indeed resembling that of a long bone, such as the radius, the stylet being articulated to the 

 head, while the distal extremity is represented by the dilated posterior end of the appa- 

 ratus. The latter has the usual granular contents, but the exterior firm investment, so charac- 

 teristically wedge-shaped in other species, does not proceed half-way forward, the slender anterior 

 portion having only a thin covering for its support. While in ordinary views the stylet and appa- 

 ratus seem straight, both have a decided curve in profile (Plate XIII, fig. 18). Just in front of 

 the point where the clear investment of the apparatus becomes indistinct, the ejaculatory duct opens 

 into the peculiarly elongated muscular cavity (e), which extends forward to the circular opening 

 in the floor of the anterior chamber. The channel shows a distinct inner layer of longitudinal 

 fibres, which, however, seem to act only in company with the external oblique series surrounding 

 them. The presence of this special coat demonstrates that it is not the mere doubling of the 

 floor of the anterior chamber which forms the cavity, as indeed certain appearances, previously 

 observed, had led me to suspect. The central and marginal 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 XI, 

 fig. 15), being sharp-pointed, then dilating gradually 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 marginal stylets show a small secondary swelling or 

 ring above the latter. The ejaculatory duct is comparatively large and distinct, comprising 

 posteriorly almost the entire region of the reservoir, a slight demarcation, however, marking 

 off the dilated extremity into a portion pertaining to the latter cavity, and another to the 

 division in front. The widened posterior end is covered with small glands, which are continued 

 along the tube to its opening in the muscular chamber behind the floor. One peculiarity 



