232 



NORMAL HISTOLOGY. 



FIG. 283. Human spermatozoa ; one head 

 is seen in profile. X 560. 



Head 



is deferred until they reach the canal of the epididymis, during the passage of which 

 long and highly tortuous path they attain maturity and lose the cytoplasmic remains 



of the spermatids that adhere for a time to the 

 middle-piece. Production of spermatozoa, which 

 occurs only within the convoluted seminiferous 

 tubules, does not involve uniformly all parts of the 

 tubule, but proceeds with wave-like periodicity; 

 consequently, cross-sections of the same tubule 

 taken a few millimeters apart exhibit different 

 stages of the spermatogenetic cycle. 



The spermatozoa or spermatic fila- 

 ments, the essential male reproductive 

 elements, are, like the ova, direct derivations 

 of the descendants of the primary indifferent 

 germ-cells. Unlike the ova, however, which 

 are relatively large and often absolutely huge 



cells, and, apart from size and minor distinctions, 



fairly similar in all vertebrates, the spermatozoa 



present great diversity in size, form and detail and 



exhibit a high degree of specialization. As ordi- 

 narily seen under moderately high magnification 



(Fig. 283), three parts may be recognized the 



head, the neck and the tail. The head is ovoid, 



flattened in front, so that when viewed in profile it 



appears pyriform. Although rich in chromatin, 



the latter is not arranged as threads or networks 



but is distributed uniformly, so that the head ap- 

 pears homogeneous. Of the 50-60 /-t representing 



the approximate entire length of the human sper- 

 matozoon, the head contributes about one-tenth 



(5-6 <i). The neck, uniting the head and the tail, 



is in man slightly constricted and, therefore, not 



easily seen, its position being indicated by the ready 



separation of the head from the tail at this point. 



It contains the minute anterior and posterior centro- 



somes or neck-granules. The tail is regarded as 



composed of three segments: the connecting piece 



(6 /0,the chief piece (40 AI) and the end 'piect ?(io//). 



The tail is traversed throughout its length by an 



extremely delicate axial fibril, which, with the ex- 

 ception of in the end piece, where the axial fibril is 



naked, is invested by an attenuated protoplasmic 



sheath. In the connecting piece (middle piece) 



the axial fibre is supposed to be surrounded by a 



spiral fibre, the posterior limit corresponding with 



a minute end-disk. Beyond the recognition of the 



chief parts of the spermatozoon the head, neck 



and tail, little can be seen of the above noted details 



unless the observer be provided with specially 



stained preparations and lenses of the highest power 



and most perfect definition. The living sperma- 

 tozoa, as seen in fresh semen, display active move- 

 ments, rapidly changing their position in consequence of the vibrations of the 



Chief piece 

 of tail 



End piece 

 of tail 



FIG. 284. Diagram illustrating 

 structural details of human sper- 

 matozoon. (At eves.) 



Axial 

 "filament 



Sheath of 



-<axia! 

 filament 



