NIERSTRASSIA FRAGILE. 239 



section, or shell gland. For a distance equal to about one fourth of its length 

 the dorsal half of the gonoduct is a simple, very slender tube but at this point it 

 enlarges somewhat and develops a short pouch-like diverticulum composed of 

 cubical, ciliated cells without any special signs of glandular activity. Contin- 

 uing its way forward for a short distance another diverticulum, finger-shaped in 

 appearance, arises and on both sides of the body is directed backward and down- 

 ward. In the usual position for the seminal receptacle a very slender tube 

 appears, on each side of the body, that is directed anteriorly for a short distance 

 and terminates in a slight enlargement. These three pairs of diverticula are 

 empty and accordingly afford no clue as regards their possible function. The 

 cells of this dorsal section of the gonoduct are all more or less cubical, cihated 

 but without ridges or other modifications. 



The shell gland, (Plate 6, fig. 5), composed of the usual long and slender 

 cells, occupies the usual position. Posteriorly the halves unite to form a single 

 median section with folded walls, but the union is unusually near the opening 

 into the cloaca. Lying ventral to this portion of the reproductive system there 

 are two bundles of spicules, five in each group, that are developed and concealed 

 in two diverticula, arising not from the cloaca, as is usual, but from the undi\'ided 

 section of the shell gland. Each of these spicules is rod-shaped, apparently 

 straight with the base rounded and the distal extremity pointed, and during 

 the act of copulation is probably protruded through the reproductive opening 

 into the cloaca. As may be seen (Plate 6, fig. 7), the median section of the shell 

 gland and the adjoining undivided portions together with the bundles of spicules 

 are imbedded in a relatively large diverticulum, rich in muscles, that in Ufe 

 may doubtless be protruded beyond the opening of the cloaca. 



In reality the cloacal chamber is comparatively large but usually it is almost 

 completely filled by the great diverticulum bearing at its tip the reproductive 

 opening. In some specimens it is partially closed and in other cases its margins 

 are widely expanded. Thi'oughout the greater part its walls are smooth and 

 unmodified but beyond the reproductive and anal openings five or six low ridges 

 (Plate 6, fig. 4) make their appearance, and while they may be respiratory they 

 certainly possess some additional unknown function since the pyriform cells 

 are highly glandular and their distal extremities are filled with a colorless secre- 

 tion after treatment with haematoxylin. In the neighborhood of the anal open- 

 ing additional groups of cells occur, and in some instances appear to open into 

 the cloacal ca\'ity, but the supposed ductules may in reality be delicate strands 

 of connective tissue. 



