866 REPRODUCTION, DEVELOPMENT, GROWTH AND DEATH [CH. L1X. 



is a much convoluted, branched, and sacculated tube of structure 

 similar to that of the vas def erens, except that the wall is thinner ; 

 their secretion is added to the semen, as is also the secretion of the 

 glands of the prostate. 



The penis is composed of cavernous tissue covered by skin. 

 The cavernous tissue is collected into three tracts, the two corpora 

 cavernosa and the corpus spongiosum in the middle line inferiorly. 



4 



5 



3 



4 



5 



FIG. 552. Semi -diagrammatic representation of 

 human spermatozoa. A, front view ; B, side 

 view. 1, Head cap surrounding head ; 2, 

 neck ; 3, body ; 4, tail ; 5, end-piece. The 

 axial filament runs through the body and 

 tail into the end-piece. 



FIG. 553. Diagram of 

 part of a human sper- 

 matozoon highly mag- 

 nified (after Meves). 

 1, Head cap ; 2, head ; 

 3, anterior centrosome 

 in neck ; 4, posterior 

 centrosome in neck ; 5, 

 axial filament; 6, spiral 

 sheath ; 7, sheath of 

 axial filament in body ; 

 8,mitochondrial sheath; 

 9, annulus ; 10, thick 

 sheath of axial filament 

 in tail. 



All these are enclosed in a capsule of fibrous and plain muscular 

 tissue; the septa which are continued in from this capsule, form 

 the boundaries of the cavernous venous spaces of the tissue. The 

 arteries run in the septa; the capillaries open into th'e venous 

 spaces. The arteries are often called helicine, as in injected specimens 

 they form twisted loops projecting into the cavernous spaces (see 

 also pp. 313, 314). 



