Ou the structure of tlie iiephriiiia of Sticlioslemma. -^7 [ 



wall, near the middle poiut of the ductule, ai)i)ears scarcely thicker 

 than a tine line, and at this portion its structure cannot be deter- 

 mined ; at its proximal end, where it is of greater diameter, it appears 

 very finely granulated (compare Figs. 1 and 7). Proximally the ductule 

 connects with the terminal bulb in such a way, that there is absolutely 

 no open communication between the cavities of the two (Fig. 7). 

 Any interchange of liquids between them must, accordingly, take place 

 by the process of osmosis. 



Main Ducts. These are bounded by ciliated epithelia, in which 

 no cell demarcations can be noticed. The cell is of a flat-cubical 

 shape, its nucleus oval, sometimes nearly spherical, with several 

 chromatic granules (Fig. 5). The cytoplasm is vacuolar, presenting 

 in general a typical honey-combed structure; the size of the vacuoles, 

 or meshes, varies noticeably in different cells, or even in different 

 portions of the same cell, and only rarely does the cytoplasm appear 

 fine-grained. This epithelium of the main ducts is bounded by a 

 basal-membrane {Bm). Of greater thickness than the latter is the 

 deeply- staining, non-refractive, homogeneous, continuous cuticula (Cut), 

 which immediately bounds the cavity of the duct. The basal-membrane 

 has been described by Bürger ('90) and others, but in no other 

 Nemertean has a cuticula been found. Each epithelial cell bears a 

 few long cilia (Cil); these are, as shown by Bürger (1. c.) simple in 

 structure, i. e. not differentiated into distinct segments, as are those 

 of the body epithelium. All these cilia are directed towards the ex- 

 cretory pores. 



Excretory Ducts. These are probably only terminal differ- 

 entiations of the main ducts, and stand in communication with the 

 outside by means of the excretory pores. Each duct (Fig, 8) is pro- 

 ximally of the same diameter as the main nephridial duct, where its 

 wall is also composed of similar nucleated cells ; but distally its cavity 

 narrows, while the lining of cells becomes gradually flattened, until 

 at its distal termination, between cells of the body epithelium, its 

 cellular wall appears only as a very fine line. No nuclei are found 

 in this distal portion. In many of the ducts an expanded ampulla 

 was present (Fig. 8 Amp). I have also not observed cilia here, though 

 these structures are probably present in life. The epithelium of the 

 duct extends not quite to the upper surface of the body epithelium. 

 That these ducts are only differentiations of the main nephridial ducts, 

 is rendered probable by the fact, that they merge gradually into one 

 another; unfortunately no conclusive observations have as yet been 



18* 



