MALE REPRODUCTIVE SYSTEM OF MAMMALS 245 



is a pair of small sac-like structures, known as the bulbo-urethral, 

 or Cowper's glands, which are present in almost all mammals, but 

 not in (logs and bears. They are large in rodents and pigs. 



IIa^•ing already considered the histology of the seminiferous 

 tubules, let us now study the other parts of the conducting system. 



Tubuli Recti.— Where the seminiferous tubule transforms into a 

 straight tul)ule, the spermatogonial cells are lacking, and the straight 

 tubules are lined with columnar cells resembling the Sertoli cells 

 of tlu' tubules. 



Rete Testis.— The irregular meshwork of these spaces is lined 

 with short cuboidal or squamous epithelium. The free surface 

 of the cells possesses a flagellum. In between the rete testis is 

 connective tissue, nerves, and vessels of the mediastinum. 



Vasa Efferentia (Tubuli Contorti), — The cells lining the ducts rest 

 upon a basement membrane and vary in size. A clump of tall, 

 ciliated columnar cells may ha\'e adjacent to them progressively 

 shorter cells. Thus, little pockets are formed in the wall of the 

 efferent ducts. At the free surface of the short type of cell is a 

 flagellum. The cells of these tubes produce a secretion which is 

 added to the mass of sperm moving through the ducts to the epi- 

 didymis. In the connective tissue outside the })asement membrane 

 there is a small amount of smooth muscle. 



Epididymis.— The hunen is larger and circular in cross-section. 

 Adjacent to the basement membrane are small cells and internal 

 to them are large columnar cells of varying heights. At the free 

 surface of each of the latter cells is a filamentous projection that is 

 non-motile Init from which secretion originating from the cytoplasm 

 of the cells is discharged into the lumen. As the epididymis ap- 

 proaches the vas deferens the columnar cells are not so tall. In 

 the connective tissue outside the basement membrane there are 

 smooth muscle cells, which constrict the tube and serve to propel 

 sperm and fluid onward toward the vas deferens. The rete testis, 

 tubuli contorti, and epididymis are portions of the old mesonephric 

 tubules used here exclusi^'ely to carry sperm. 



Vas Deferens. (Fig. lol.) This is a larger tube than the epi- 

 didymis and its lumen is also greater. The epithelium of its mucous 

 membrane is of the stratified columnar variety. The tunica propria 

 has long folds which make the lumen irregular in shape. There is 

 no definite submucosa, but outside the tunica propria is a muscle 

 coat which consists of a thin innermost coat in which the smooth 

 muscle cells are arranged lengthwise of the tube, a relatively thick 

 middle circular coat of muscle, and an outer longitudinal coat which 



