288 Vertebrate Embryology 



The human spermatozoon (Fig. 86) re- 

 sembles, in a general way, the spermatozoa of 

 the other mammalia. Its most evident parts 

 are the head, middle-piece, and tail. Besides 

 these an end-piece may be made out, under 

 high magnifications, and some observers have 

 described a thread-like tip at the anterior end 

 of the head. The length of the entire sper- 

 matozoon is between .05 and .06 mm. The 

 head is oval in outline, as seen from the flat 

 side, and is pointed when seen in profile 

 (Fig. 86, B)\ it stains darkly with nuclear 

 stains. The middle-piece is the anterior por- 

 tion of the tail, where it joins the broad, 

 basal part of the head ; it is cylindrical in 

 shape and is thicker than the tail proper, 

 from which it is sharply differentiated. The 

 tail forms the greater part of the length of 

 the spermatozoon, and ends suddenly in the 

 short and extremely fine end-piece. The tail 

 of the living spermatozoon vibrates rapidly, 

 thus acting as a propeller to produce forward 

 motion. 



As in the case of oogenesis, so here the 

 reader is referred to larger works on embry- 

 ology or to text-books of histology for a dis- 

 cussion of the process of spermatogenesis. 



