SPERMATIC DUCTS. 231 



becomes gradually excentric and assumes a long, oval form. In 

 the early stages of the change the spermatids contain two cen- 

 trosomes which have a quite superficial situation. From the 

 more superficial (distal) of these there grows out from the cell 

 a delicate thread of protoplasm, which is the very beginning 

 of the tail (Fig. 178, a). The centrosome lying nearer the 

 nucleus (proximal) becomes rod-shaped, while the one outside 

 assumes a conical form. Both centrosomes approach the 

 nucleus and the proximal one unites with it. The distal 

 conical centrosome is differentiated into two structures, a bulb 

 and a ring (Fig. 178). The ring moves back along the tail 

 axis until it reaches the periphery of the cell. This divides 

 the middle piece from the chief segment of the tail (Fig. 178, 

 /and g). The significance of the capsule is not clear. In the 

 middle piece it probably represents the remains of a part of the 

 cell protoplasm. From this last stage the fully formed sper- 

 matozoa may readily be traced (Fig. 178). 



B. Spermatic Ducts. 



From the rete testis proceed the ductuli efferentes testis, or 

 vasa efferentia, which break through the tunica albuginea and 

 form a part of the epididymis. There are from nine to fifteen 

 of these, and each forms by its tortuous course a lobule sur- 

 rounded by connective tissue (lobuli epididymis, coni vasculosi 

 Halleri). All the lobules together form the head of the epi- 

 didymis. The vasa efferentia join to form the vas epididymis, 

 which takes a very complicated, coiled course and makes up the 

 body and tail of the epididymis, finally opening into the vas 

 deferens. 



The vasa efferentia are lined with two kinds of epithelium, 

 one composed of high columnar ciliated cells containing yellow 

 granules, and the other made up of cubical non-ciliated cells. 

 These are arranged in rows and concentrated in groups. The 

 groups of cubical cells form swellings among the cylindrical 

 cells, and have the appearance of intra-epithelial alveolar 

 glands. Outside the membrana propria there are smooth 

 muscle cells arranged in circular layers. Some authors have 



