820 



THE REPRODUCTIVE ORGANS 



[CH. LVIII. 



ovoid shape, and in the anterior two-thirds of its extent is surmounted 

 by a head-cap which, sharpened at its extremity, forms a cutting 

 edge. The neck is very short, but contains two centrosomes. The 

 body is about the same length as the head ; it is traversed by an 

 axial filament and a spiral fibril wound round the sheath of the 

 axial? filament. More externally is a layer of punctiform substance 



4 



5 





4 



5 



FIG. 611. 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. 612. Diagram of 

 part of a human sper- 

 matozoon highly mag- 

 nified (after Meves). 

 1, Head cap ; 2, head ; 

 3, anterior controsome 

 in neck ; 4, posterior 

 centrosome in neck ; 5, 

 axial filament; 6, spiral 

 sheath ; 7, sheath of 

 axial filament in body ; 



8, mitochondria! sheath; 



9, annulus ; 10, thick 

 sheath of axial filament 

 in tail. 



called the mitochondrial sheath which terminates at the junction 

 with the tail on an annular disc. The axial filament is continued 

 through the tail into . the end - piece, and in the tail is sur- 

 rounded by thick sheath. In some animals, newts and sala- 

 manders, the tail is surrounded by a spiral membrane, but this 

 is not present in the human spermatozoon. The head of the 

 spermatozoon is formed from the nucleus of the spermatid, the 

 head-cap from the idiosome; the centrosomes jof the spermatid 



