ON MONOPYLEPHORÜS LIMOSUS. 29 



and lie always in the dorsal region of the body. The anterior 

 sperm- sac originates from the anterior septum and lies in segment 

 IX, while the posterior one is formed by the posterior septum and 

 extends backwards, sometimes to segment XVII. The walls of the 

 sperm-sacs are very thin and structureless. 



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

 a short narrow vas deferens, a spindle-shaped atrium with diffusely 

 scattered prostate cells, an atrial duct portion and a spermiducal 

 chamber (fig. 24). The whole organ with the exception of the 

 funnel lies in segment XL 



The sperm- duct funnel is wide and is attached to the anterior 

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

 ventral blood-vessel. Its shape is somewhat urceolate and the 

 nephrostome is directed dorso- laterally close to the ventral median 

 line of the body. The wall of the funnel mostly shows irregular 

 foldings and consists of two layers. The inner layer consists of 

 regularly arranged, ciliated, very narrow columnar cells, which are 

 very vesicular and contain in the distal part a small amount of 

 cytoplasm usually forming strands. The cilia are all of nearly equal 

 lengths. The nuclei are compact, long, and invariably situated in 

 the proximal part of the cells, with their length perpendicular to 

 the surface of the funnel. The outer layer is formed by the con- 

 nective tissue derived from the peritoneum. 



The funnel is continued into a short slender vas deferens, which 

 pierces septum X/XI at its beginning. The latter is circular in 

 cross section all through, and its diameter increases gradually from 

 20 [i to 25 p- as it proceeds posteriorly. Its lumen is very narrow, 

 measuring about one-fifth or one-sixth of the diameter. The wall 

 of the tube consists, as in the funnel, of two layers, the inner of 

 which is composed of ciliated cubical cells, each containing a round 

 nucleus and a cytoplasm which is simply finely and uniformly granular. 



