THE REPRODUCTIVE SYSTEM 



349 



connect with the more dehnite lymph vessels of the mediastinum and 

 of the spermatic cord. 



Nerves. — Non-meduUated nerve fibres form plexuses around the 

 blood-vessels. From these, fibres 

 pass to plexuses among the semi- 

 niferous tubules. Their exact 

 method of termination in connec- 

 tion with the epithelium has not 

 been determined. In the epidid- 

 ymis are found small sympathetic 



Head < 



ganglia. The walls of the vasa 



Galea 

 capitis 



Neck 



Body - 



End ring ■ 



I 



Main segment 

 of tail 



Anterior end knob 

 Posterior end knob 



Spiral fibers 



Sheath of 

 ' axial thread 



Axial thread 

 Capsule 



efferentia, vas epididymis, and vas 

 deferens contain plexuses of non- 

 medullated nerve fibres, which give 

 off terminals to the smooth muscle 

 cells and to the mucosa. 



The Spermatozoa. — The 

 spermatozoa are the specific secre- 

 tion of the testicle. Human 

 spermatozoa are long, slender 

 flagellate bodies, from 50 to 70/1 

 in length, and are suspended in 

 the semen, which is a secretion of 

 the accessory sexual glands. The 

 general shape is that of a tadpole; 

 and by means of an undulatory 

 motion of the tail, the spermato- 

 zoon is capable of swimming about 

 freely in a suitable medium. It 

 has been estimated that the human 

 spermatozoa average about sixty 

 thousand per cubic millimetre of 

 semen. 



The human spermatozoon con- 

 sists of (i) a head, (2) a middle 

 piece or body, and (3) a tail or 

 flagellum (Fig. 244). 



The head, from 3 to 5,« long and about half that in breadth, is oval 

 in shape when seen on flat, pearshaped when seen on edge. It con- 

 sists mainly of chromatin drived from the nucleus of the parent cell. 



Terminal 

 filament 



Fig. 244. — Diagram of a Human Sper- 

 matozoon. (Meves, Bonnet.) 



