THE SPERMATOZOON 



43 



chromatin, and is generally regarded as the nucleus of the cell surrounded by a 

 thin envelope. 



The neck is less constricted in the human spermatozoon than in those of some 

 of the lower animals. The anterior centriole, represented by two or three rounded 

 particles, is situated at the junction of the head and neck, and behind it is a band 

 of homogeneous substance. 



The connecting piece or body is rod-like, and is limited behind by a terminal 

 disk. The posterior centriole is placed at the junction of the body and neck and, 

 like the anterior, consists of two or three rounded particles. From this centriole 

 an axial filament, surrounded by a sheath, runs backward through the body and 

 tail. In the body the sheath of the axial filament is encircled by a spiral thread, 

 around which is an envelope containing mitochondria granules, and termed the 

 mitochondria sheath. 



The tail is of great length, and consists of the axial thread or filament, sur- 

 rounded by its sheath, which may contain a spiral thread or may present a striated 

 appearance. The terminal portion or end-piece of the tail consists of the axial 

 filament only. 



Primary cocyte 



Primary spcrmatocytc 



Secondary ( } 

 oocyte 



Mature 



O Secondary 

 spermatocytes 



O 



OoooQO OO 



Polar bodies 



Spermatids 



Pia. 7. Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids 



(young spermatozoa). 



Krause gives the length of the human spermatozoon as between 52/x and 62/i, 

 the head measuring 4 to 5/i, the connecting piece 6/z, and the tail from 41^ to 52/z. 



By virtue of their tails, which act as propellers, the spermatozoa are capable of 

 free movement, and if placed in favorable surroundings, e. g., in the female pas- 

 sages, will retain their vitality and power of fertilizing for several days. In certain 

 animals, e. g., bats, it has been proved that spermatozoa retained in the female 

 passages for several months are capable of fertilizing. 



The spermatozoa are developed from the primitive germ cells which have become 

 imbedded in the testes, and the stages of their development are very similar to those 

 of the maturation of the ovum. The primary germ cells undergo division and 

 produce a number of cells termed spermatogonia, and from these the primary 

 spermatocytes are derived. Each primary spermatocyte divides into two secondary 

 spermatocytes, and each secondary spermatocyte into two spermatids or young 

 spermatozoa; from this it will be seen that a primary spermatocyte gives rise to 

 four spermatozoa. On comparing this process with that of the maturation of the 

 ovum (Fig. 7) it will be observed that the primary spermatocyte gives rise to 

 two cells, the secondary spermatocytes, and the primary oocyte to two cells, the 

 secondary oocyte and the first polar body. Again, the two secondary sperma- 



