680 



THE REPRODUCTIVE ORGANS 



The sperm cells are the essential male reproductive cells. Each sperma- 

 tozoan consists of a minute oval head, a middle piece, and a tail. The head 

 is 4 /* by 2.5 P. The middle piece and tail are about 50 to 60 M long. 

 Sperm cells possess the power of flagellate movement. 



The Vas Deferens. This is the single duct proceeding from each 

 testicle to join its fellow at the base of the bladder. Each has an ampulla or 



spc.i 



FIG. 488. Later Stages in Spermatogenesis of the Bull, spg.r, Reserve spermatogonium; 

 spg, spermatogonium; spc.g, spermatocyte in late synapsis stage; spc.i, spermacyte in stage just 

 preceding the maturation divisions; spd, spermatids in advanced stage of histogenesis, with 

 heads deeply embedded in Sertoli cell. Highly magnified. (After Schoenfeld.) 



enlargement just before it unites with its fellow. The vas deferens has muscu- 

 lar walls and is lined with ciliated epithelial cells. 



The Vesiculae Seminales. The seminal vesicles have the appear- 

 ance of outgrowths from the base of the vasa deferentia. Each vas deferens, 

 just before it enters the prostate gland, through part of which it passes to 

 terminate in the urethra, gives off a side branch which bends back from it at 

 an acute angle. This branch, dilating, variously branching, and pursuing in 



