SPECIES OP THE GENUS AULODRILUS. 



955 



The vas deferens is a short slightly curved tube leading back 

 from the seminal funnel and opening behind into the anterior 

 end near the ventral margin of a somewhat swollen chamber, the 

 atrium. The duct is circular in transvei'se section, and of nearly 

 the same breadth throughout, i. e. about 25 jj.. The lumen is only 

 4 fx in diameter. It is lined by cubical epithelial cells of 7*5 /x 

 height and without definite cell-outlines ; the oval nuclei of 7"5 fj. 

 greatest diameter lie at right angles to tlie height of the cells. 

 Outside the epithelium there is present a thin layer of circular 

 muscle fibres, which as the seixjinal duct joins the atrium becomes 

 much thicker and is continued into the thick muscular coat of 

 the ati-ium. A few nuclei seen in sections here and there outside 

 the muscular layer indicate the presence of the peritoneal layer. 



Text-fisfure 4. 



p.str.d. 



d.atr.d. 



Semi-diagrammatic vertical section of the vas deferens apparatus as 

 compiled from several successive sections. X ca. 540. 



In the earl}^ stage the vas deferens is shorter and runs nearly 

 shraight to open at the anterior end of the atrium ; it is also 

 narrower, the breadth then being only about 14^ including a 

 lumen of 2*5 /a. The epithelial cells are cubical, the muscular 

 coat around the epithelium is feebly developed or even in a still 

 earlier stage absent. The epithelial cells of the vas deferens are 

 altogether devoid of cilia, while in the case of Tuhifex tuhifex and 

 Limnodrilus daparedeianus the cilia are quite conspicuous. In 

 the latter genus I had the opportunity of examining the A^as 

 deferens on several occasions and found the epithelium provided 

 with long cilia ai'ising from the basal granules, which are visible 

 in the living worm under a high power. It is also intei-esting to 

 note here, that the vas deferens throughout the sexual phase is 

 short. 



