TRICI.An TURRia.I.ARIA FRIIM INDIAN TIHET y 



and bnlb should not be considered as separate parts of the copulatory apparatus but as one 

 structure. 



In the L 25 specimen, whicli seems the most mature of the four, the penis bulb is a 

 rounded hollow sac of moderate dimensions immediately behind the bursa copulatrix (Plate I, 

 fig. 7, pb). It is well-defined and plainly marked off from the surrounding tissues but is not 

 strikingly muscular. The wall is of moderate thickness and composed chiefly of muscle fibers 

 coursing in several directions. The interior is hollow forming a seminal vesicle (Plate II, 

 fig. 4, sv), somewhat hourglass-shaped in transverse section owing to the projection into the 

 lumen of the two lateral papillae which bear the ternn'nations of the vasa deferentia (Plate I, 

 fig. 8, and Plate II, fig. 4). The lumen is lined by what appears to be a glandular epithelium 

 densely packed with secretion granules. However, under oil immersions, the epithelial cells 

 are found to be practically undetectable owing to their penetration by what appear to be tubes 

 packed with coarse granules (Plate II, fig. 2). Similar granules in groups are found through- 

 out the subepithelial wall of the bulb as well as in adjacent tissues. It appears probable that 

 <ve are dealing with very long-stalked unicellular glands which open by ducts through the 

 lining epithelium of the bulb. These ducts project beyond the epithelial surface and often 

 a cloud of granules is seen emerging from their open ends (Plate II, fig. 2). These granule- 

 filled ducts have been found only in the very ripe L 25 specimen and seem to indicate that 

 some secretion of importance is discharged into the seminal vesicle during the height of 

 sexual activity. 



In the L25 specimens, the penis is a short weak cone-shaped organ projecting into the 

 male atrium (Plate I, fig. 7) and containing a short duct running from the seminal vesicle 

 to the tip of the penis. The duct is lined by a columnar epithelium lacking the granular 

 tubes mentioned above. The male atrium is lined by a cuboidal epithelium encircled by cir- 

 cular, longitudinal, and radial muscle fillers (Plate II, fig. 1). It is expanded where it con- 

 tains the penis but immediately beyond this organ narrows at once to a short canal which 

 receives in its middorsal line first the common oviduct and then the stalk of the bursa 

 (Plate I, fig. 7). It then immediately opens at the genital pore, the common cavity formed 

 by its union with the bursa stalk being thus so small as scarcely to merit the name of common 

 atrium. All of these relations in the atrium are typical of the genus Polycelis. 



As already indicated the appearance of penis bulb and penis is very different in the 

 K 78 specimens (Plate II, fig. 3). Here the penis bulb is apparently contracted and forms a 

 muscular mass at the base of the penis. The seminal vesicle seems to have been projected 

 into the penis but its boundaries are still determinable by means of the papillae on which the 

 vasa deferentia terminate. The penis in consequence of having incorporated most of the penis 

 bulb appears very much larger, longer and more powerful than when at rest (compare Plate I, 

 fig. 7, and Plate II, fig. 3j. - The conditions in these specimens seem to prove that the penis 

 bulb is of great help in the extrusion of the penis and is really an essential part of that organ. 



The bursa copulatrix in all the specimens is a large, irregularly rounded sac lying between 

 the rear end of the pharynx and the penis bulb, and considerably larger than the latter .struc- 

 ture (Plate I, fig. 7). Its histology is typical, the organ being lined by the usual large 

 bulbous epithelial cells containing rounded masses. From the center of its posterior surface 

 the stalk arises and runs posteriorly above the penis bulb. At first the stalk is large and lined 

 by the same epithelium as the bulb; but at about the level of the union of the oviducts, the 

 stalk narniws abruptly (Plate I, fig. 7, and Plate II, fig. 3) and its epithelium becomes of an 



