TWO AQUATIC OUGOCH JETES. 27 



reaching to segment XVI. Sometimes the anterior sperm- sacs 

 are unequally developed, but are never united. 



The walls of the sperm- sacs are very thin and structureless, 

 but are richly supplied with blood capillaries in mature specimens, 

 either on the outer or inner side. 



3). Sperm-ducts. Each sperm-duct consists of a wide 

 funnel, a long narrow vas deferens, a spindle-shaped atrium with 

 a glandular appendage, the ' prostate,' and a duct portion and a 

 penis. The whole organ with the exception of the funnel lies in 

 segment XI. 



a. Funnel. The funnel is the internal opening of the 

 sperm-duct ; it is very wide and is attached to the anterior face 

 of septum X/XI in segment X, on either side of the ventral 

 median line. Its shape is somewhat urceolate, and the margin 

 mostly shows irregular foldings. 



The wall of the funnel consists of two layers. The inner 

 layer consists of regularly arranged, ciliated columnar cells, 

 measuring 10-12/« by 4—5;«.. They are very vesicular and con- 

 tain in the distal part a small amount of feebly staining cyto- 

 plasm, which usually forms strands to support the layer against 

 the pressure of the sperm. The cilia are all of nearly equal 

 lengths, measuring 5-7 /a The nuclei, sometimes containing a 

 single nucleolus, are in Indian specimens situated invariably in 

 the proximal part of the cells, while in Japanese ones they lie 

 invariably in the middle of the cells. This is the only point in 

 which the two sets of specimens differ from each other. The 

 outer layer of the funnel is formed by the connective tissue 

 derived from the peritoneum. 



b. Vas deferens. The funnel is continued into a very long, 

 slender vas deferens, which undergoes several windings. It is 

 circular in cross -section and of uniform diameter all through, viz. 

 about 25 p-. The lumen is about one third of the diameter, except 

 for a short distance at the beginning, where it is wider. The tube 

 is attached to the septum only at its beginning, while the remainder 

 lies free in the cœlom, and consequently assumes several positions 

 between other organs, and often extends into segment XII. 



