1946 



HUMAN ANATOMY. 



The spermatic filaments or spermatozoa, the essential male reproductive 

 elements, are, like the ova, direct derivations of epithelial cells that are descendants 



Fig. 1657. 



Diagram illustrating phases of one complete cycle of spermatogenesis. Sequence of figures shows in 

 detail growth (1-6) and division (7-8) of spermatogone; growth and division of primary spermatocyte (9-19) 

 into secondary spermatocytes; division of latter (20-21) into spermatids (22-24); fusion of these with Sertoli cell 

 to form spermatoblast (25-26); differentiation (27-31) and final liberation (32) of spermatozoa. (After Ebner.) 



of the primary indifferent sexual elements. Unlike the ova, however, which are rela- 

 tively large and often absolutely huge, and, apart from size and minor distinctions, 



fairly similar in all vertebrates, the sper- 

 Ftg. 1638 matic filaments present great diversity 



in form and detail and represent a high 

 degree of specialization. The human 

 spermatic filament is small, and consists 

 of an ovoid head, a cylindrical tniddle- 

 piece of uncertain extent, and a greatly 

 attenuated and prolonged tail, — the 

 propelling organ of the flagellated cell. 

 The mature element measures about 

 .050 mm. in its entire length, of which 

 only about .005 mm. is contributed by 

 the head, probably about the same by 

 the middle-piece, and from .040-. 045 

 mm. by the tail. The head, somewhat 

 flattened in front and hence pyriform 

 in profile, although rich in chromatin, 

 appears homogeneous, since the chro- 

 matin is uniformly distributed and not 

 arranged as threads or mesh -works. 

 The structural basis of the remaining parts of the spermatic element is a delicate 

 axial fibre that extends from the head to the tip of the tail (Fig. 12) and is in- 



Human spermatic filaments seen from the broad sur- 

 face, except a, which is in profile.  Soo. 



