ON A PRORHYNCHID TQRBELLARIAN. 639 



aperture is a small slit situated in a recess below the pharynx, 

 this recess opening on the exterior through the mouth. The 

 penis (figs. 1, 5, and 6) is a long and slender, pointed, chitinous 

 spine. Contained within the lumen of the penis is a finely 

 fibrillated material, which stains faintly with eosin. Investing 

 it is a layer of fine fibres, most of which take a spiral course. 

 This layer is continuous at the base of the penis with the wall 

 of the ejaculatory duct, while at the apex it is continuous with 

 the penis sheath ; between it and the penis on the one hand, 

 and the penis sheath on the other, are several large nuclei. 

 The sheath of the penis consists of an outer layer of circular 

 fibres, and an inner of longitudinal ; the latter is a continuous 

 layer in the greater part of its extent, but divided towards the 

 apex of the penis into a number of distinct bundles. Sup- 

 porting the sheath are ten slender chitinous rods, which, where 

 the sheath is reflected in front to become continuous with the 

 investing layer of the penis, bend sharply backwards for some 

 distance. 



The ejaculatory duct presents a slight bulbous dilatation at 

 the base of the penis. It is a thick-walled tube with a 

 muscular wall, composed mostly of circular fibres. The penis 

 sheath is continued over it for a short distance, but stops short 

 completely before reaching the vesicula seminalis. The vesi- 

 cula seminalis (fig. 1, v. s.) is a very large sac of long oval 

 form. Its walls are thick and muscular, the fibres taking for 

 the most part an oblique direction round the wall. In the 

 interior is a thick layer of a finely fibrillated substance bound- 

 ing a relatively narrow central lumen. At the junction of the 

 ejaculatory duct and vesicula open the ducts of a number of 

 unicellular glands, which probably are the prostate or granule 

 glands. From the vesicula runs a very greatly coiled narrow 

 duct, the vas deferens. This becomes somewhat thicker 

 posteriorly, and eventually is continued into a wide thin- 

 walled spirally twisted sac, the sperm reservoir {sp. r.) — com- 

 pletely filled, in all three mature specimens, with ripe sperms. 

 From this a short, straight, narrow efferent duct leads 

 obliquely towards the left, where it enters the testis, and is 



